•RADIO 
TELEPHONY 


BY 


ALFRED   N.   GOLDSMITH,  Ph.  D, 

Fellow  of  the  Institute  of  Radio  Engineers 
Member  of  the  American  Institute  of  Electrical  Engineers 


Director  of  the  Radio 
Telegraphic  and  Telephonic  Laboratory 

and  Professor  at 
The  College  of  the  City  of  New  York 


THE  WIRELESS   PRESS,  Inc. 

25  Elm  Street,  New  York 


Copyright,  1918 
By  WIRELESS  PRESS,  Inc. 


CONTENTS 

(Classified  Topically  and  According  to  Chapters) 


CHAPTER  I  ..........................................  . 

1.  WORLD  ASPECTS. 

2.  PERSONAL  ASPECTS. 

3.  USES  OF  RADIO  TELEPHONY. 

(a)  SHIP-TO-SHIP  AND   SHIP-TO-  SHORE. 

(b)  TRANS-OCEANIC  AND  TRANS-CONTINENTAL. 

(c)  EXCEPTIONAL  REGIONS. 

(d)  TRAIN-TO-TRAIN    AND   TRAIN-TO  STATION. 

(e)  UNDERGROUND,  AEROPLANE,  SUBMARIN^    ETC. 

4.  RADIO  VERSUS  WIRE  TELEPHONY. 

(a)  FOR    LAND    TELEPHONY. 

(b)  FOR    OVERSEA    TELEPHONY. 

5.  BROAD    PROBLEMS    INVOLVED    IN   RADIO   TELE- 

PHONY 

(a)  RADIATION  OF  MODULATED  ENERGY. 

(b)  CAUSES  OF  SPEECH  DISTORTION  —  "electrical  inertia"  —  receiver 

distortion  —  transmitter   distortion. 

(c)  NON-LINEAR   AMPLIFICATION   AND    SPEECH   DISTORTION  —  types 

of  distortion. 

(d)  SECRECY  OF   COMMUNICATION   IN   RADIO  TELEPHONY. 

(e)  STRAY    INTERFERENCE    IN    RADIO    TELEPHONY  —  "transmission 

factor   of  safety"  —  "assistance  of  context." 


CHAPTER  II  ..............................................  ............     21 

6.    SUSTAINED  .WAVE  GENERATORS. 

(a)  ARCS  —  Diiddell-Poulsen  arc  —  Poulsen  arc  —  Fuller's  method 

of  increasing  output  efficiency  —  arcs  of  Danish  Conti- 
nental Syndicate  —  "flywheel  circuit"  —  arcs  of  Berliner 
Company  —  arcs  of  Lorenz  Company  —  arcs  of  Federal 
Telegraph  Company  —  experiments  of  Majorana  —  arcs  of 
Telefunken  Company  —  arcs  of  Colin  and  Jeance. 

CHAPTER  III  .........................................................     44 

(b)  RADIO-FREQUENT     SPARKS  —  inverse     charge     frequency  —  ex- 

periments of  Ruhmer  —  experiments  of  Dubilier  —  Lorenz 
Comoany  "multitone"  system  —  system  of  von  Lepel  —  ex- 
periments of  Chaffee,  and  Cutting  and  Washington— 
Ditcham  system  —  T.  Y.  K.  system  —  Hanscom  transmitter 
-de  Forest  D.  C.  and  A.  C.  systems—  experiments  of 
Moretti  —  experiments  of  Vanni  —  experiments  of  Gold- 
schmidt  and  Scheidt-Boon  —  experiments  of  Marzi 
brothers  —  Marconi's  "timed  spark"  method. 

Ill 


IV  Contents 

CHAPTER  IV  ........................................................  .     76 

(c)  VACUUM    TUBE   OSCILLATORS  —  Dushman's    data  —  temperature 

and  space  charge  limitation  of  plate  current  —  thermionic 
currents  in  filament  —  White  filament  supply  method  — 
grid  potential  control  of  plate  current  —  tube  amplifica- 
tion of  alternating  current  —  self-excited  oscillations  —  os- 
cillating circuit  of  Meissner  —  Marconi-Franklin  circuits 

—  de   Forest   ultraudion  and   other   circuits  —  high   power 
tubes  —  General    Electric    Company    pliotrons  —  oscillating 
circuit   of   General   Electric  Company—  Western   Electric 
Company  tubes  —  experiments  of  Colpitts  —  experiments  of 
Heising  —  Nicolson  tube  —  General   Electric   Company  dy- 
natron  and  pliodynatron  —  Hull's  dynatron  amplifier  and 
oscillator  —  Hull's    pliodynatron    controlled    oscillator. 

CHAPTER  V  ..........................................................   103 

(d)  ALTERNATORS  OF  RADIO  FREQUENCY  —  problem  of  construction 

—  types    of    solution  —  Goldschmidt    alternator  —  frequency 
multiplication  by  "internal  reflection"  —  constructional  de- 
tails —  principle    of   ferromagnetic    frequency   multiplier  — 
Telefunken   Company   frequency   doublers   and  triplers  — 
Arco  alternator  of  Telefunken  Company  —  Alexanderson 
alternator  —  constructional     details  —  electrical     character- 
istics —  Experiments  of  Fessenden  and  National  Electric 
Signaling    Company  —  experiments    of    General    Electric 
Company  —  Alexanderson   triple    frequency   alternator. 

CHAPTER  VI  .........................................................  127 

7.    MODULATION  CONTROL  IN  RADIO  TELEPHONY. 

(a)  DEGREE  OF   CONTROL  —  modulation   characteristic  —  linear  and 

non-linear    modulation    control  —  actual    characteristic. 
STABILITY  OF  CONTROL  —  static  and  dynamic   characteristics. 
RATING  OF  RADIOPHONE  TRANSMITTERS. 

(d)  TYPES  OF  CONTROL. 

(e)  MICROPHONE  TRANSMITTER  CONTROL  —  single  microphone  con- 

trol —  multiple  microphone  control  —  methods  of  Lorenz 
Company  and  Goldschmidt  —  method  of  Ditcham. 

(f)  HIGH  CURRENT  MICROPHONES  —  Fesscnden's  telephone  relays 

—  condenser  transmitters  and  method  of  use  —  Dubilier's 
relay  —  Berliner  Company  high  current  microphone  —  Eg- 
ner-Holmstrom   high   current  microphone  —  Scheidt-Boon 
Marzi   microphone  —  Chamber's   liquid   microphone  —  yan- 
ni's    liquid    transmitter  —  Majorana's    liquid    transmitter 
and  experiments  therewith. 

CHAPTER  VII  ........................................................  153 

(g)  VACUUM  TUBE  CONTROL  SYSTEMS  —  general  methods  —  Meiss- 

ner radiophone  —  characteristic  of  tube  containing  gas  — 
Marconi  Company  transmitter  —  circuits  of  Round  —  ex- 
periments and  transmitters  of  de  Forest  and  Logwood  — 
transmitters  of  Western  Electric  Company  —  modulating 
system  of  Colpitts  —  system  of  Heising  —  transmitters  o£ 
General  Electric  Company  —  modulating  system  of  White  — 
Hull  pliodynatron  transmitters  —  composite  Alexander- 
son  alternator  and  pliotron  systems  —  types  of  absorption 
modulation  —  influence  of  modulation  on  selectivity. 


(b) 
(c) 


Contents  V 

CHAPTER  VIII 182 

(h)  FERROMAGNETIC  CONTROL  SYSTEMS — experiments  of  K>'ihn — 
multiple  microphone  preliminary  control — radio  frequency 
choke  coil  combinations — Telefunken  Company  transmit- 
ters— Alexanderson  telephone  relay — Alexanderson  mag- 
netic amplifier — magnetic  amplifier  circuits — magnetic 
amplifier  characteristics  of  control  and  stability — work 
of  General  Electric  Company. 

(i)  COMPARISON  OF  CONTROL  SYSTEMS — for  low  powers — for  mod- 
erate powers — for  high  powers. 

CHAPTER  IX 205 

8.  ANTENNAS  AND  GROUND  CONNECTIONS. 

(a)  RADIATING  SYSTEMS — antenna  radiation  efficiency. 

9.  RECEPTION  PHENOMENA. 

(a)  DETECTOR  AND  AMPLIFIER  TYPES. 

(b)  BEAT  RECEPTION — constancy  of  radiated  frequency. 

(c)  SELECTIVITY  IN  RECEPTION. 

(d)  INTERFERENCE  WITH  RADIOPHONE  RECEPTION. 

(e)  TELEPHONE  RECEIVERS. 

(f)  RECEIVING  APPARATUS — audion  receivers — Armstrong  regen- 

erative receivers — ultraudion  circuit — Telefunken  Com- 
pany— Meissner  receiving  arrangements — Marconi  Com- 
pany receiver — Western  Electric  Company  tubes  for 
reception — tube  designs  of  van  der  Bijl,  Nicolson,  and 
Hull— General  Electric  Company  tubes  for  reception  and. 
amplification  (pliotrons). 

(g)  STRAYS — Balanced  valve  receivers — Dieckmann  cage — Clas- 

sification of  strays — compensation  method  of  stray  re- 
duction— methods  of  de  Groot. 

(h)  RANGE  IN  RADIO  TELEPHONY — occasional  range — reliable 
range — annual  increase  in  range. 

CHAPTER  X 230 

10.    RADIOPHONE  TRAFFIC  AND  ITS  REGULATION. 

(a)  DUPLEX   OPERATION — method   of   Marconi — method   of  Fes- 

senden — method  of  Carson. 

(b)  SHIP-TO-SHORE  RADIO  TELEPHONY. 

(c)  LONG    DISTANCE    RADIO    TELEPHONY — rates — radio    telephony 

versus    rapid    radio    telegraphy. 

(d)  FUTURE  DEVELOPMENT  OF  RADIO  TELEPHONY. 

INDEX  OF  INVESTIGATORS  AND  TOPICS..  ...  243 


PREFACE 

SINCE  the  publication  of  Dr.  Erskine-Murray 's  excellent  translation 
of  Ruhmer's  "Drahtlose  Telephonic,"  there  has  appeared  no  com- 
plete exposition  in  any  language,  so  far  as  the  author  is  aware,  of 
the  important  and  growing  field  of  radio  telephony.    The  date  of  publica- 
tion of  Ruhmer's  book  was  1907,  and  in  the  succeeding  decade  advances 
have  been  made  which  render  the  methods  there  described  obsolete. 

Accordingly  the  author  has  accepted  the  considerable  task  of  writing 
a  full  description  of  the  radio  telephonic  methods  of  the  present  in  the 
thought  that  he  might  thus  contribute  to  progress  in  that  valuable  art. 
Wherever  possible,  sufficiently  complete  descriptions  of  the  apparatus 
employed  have  been  given  to  enable  the  "person  skilled  in  the  art"  to 
duplicate  the  results  and  to  judge  their  value.  In  this  connection,  the 
ranges  of  transmission  and  the  output  power  of  the  radiophonic  stations 
have  been  presented.  It  has  been  thought,  too,  that  the  arrangement  of 
apparatus  in  the  set  was  of  value  in  that  it  indicated  how  the  various 
designers  had  attacked  the  problem  of  making  radiophonic  apparatus 
readily  usable. 

It  need  hardly  be  stated  that  a  good  working  knowledge  of  the 
methods  and  principles  of  modern  radio  telegraphy  is  necessary  for  the 
full  appreciation  of  the  material  here  set  forth,  though  certain  questions . 
common  to  both  types  of  communication  have  been  here  considered  in 
detail. 

The  author  desires  to  express  his  deep  indebtedness  for  the  valuable 
assistance  in  the  form  of  information,  illustrations,  and  diagrams  which 
he  has  received  from  the  following  gentlemen  and  the  organizations  with 
which  they  are  connected: 
Atlantic  Communication  Company  and  Messrs.  Boehme,  Brockmann  and 

Reuthe ; 
Compagnie  Generale  de  Radiotelegraphie,   and  Lieutenants  Colin  and 

Jeance  of  the  French  Navy; 
Lieutenant  W.  Ditcham  of  the  British  Army; 
Mr.  William  Dubilier; 

Federal  Telegraph  Company  and  Mr.  Leonard  F.  Fuller; 
General  Electric  Company  and  Messrs.  E.  F.  W.  Alexanderson,  Albert 

W.  Hull,  and  William  C.  White ; 
Mr.  W.  Hanscom; 
Marconi   Wireless   Telegraph   Company  of  America   and   Mr.   Roy   A. 

Weagant ; 

National  Electric  Signaling  Company  and  Mr.  John  L.  Hogan,  Jr. ; 
Radio  Telephone  and  Telegraph  Company  and  Dr.  Lee  de  Forest; 
Mr.  Bowden  Washington ; 
Mr.  Eitaro  Yokoyama. 

Through  their  kindness  he  has  been  enabled  to  present  here  much  im- 
portant information  and  previously  unpublished  material. 

He  also  desires  to  commend  highly  the  painstaking  efforts  of  the 
editors  of  The  Wireless  Press  to  make  this  book  measure  up  to  the  high 
aims  of  that  organization. 

ALFRED  N.  GOLDSMITH. 


RADIO  TELEPHONY. 
CHAPTER  I. 

1.  WORLD  ASPECTS.  2.  PERSONAL  ASPECTS.  3.  USES  OF 
RADIO  TELEPHONY — (a)  SHIP-TO-SHIP  AND  SHIP-TO-SHORE. 
(b)  TRANS-OCEANIC  AND  TRANS- CONTINENTAL.  (c)  EX- 
CEPTIONAL REGIONS,  (d)  TRAIN-TO-TRAIN  AND  TRAIN-TO- 
STATION,  (e)  UNDERGROUND,  AEROPLANE,  SUBMARINE,  ETC. 
4.  RADIO  VERSUS  WIRE  TELEPHONY — (a)  FOR  LAND  TELE- 
PHONY, (b)  FOR  OVERSEA  TELEPHONY.  5.  BROAD  PROB- 
LEMS INVOLVED  IN  RADIO  TELEPHONY — '(a)  RADIATION  OF 
MODULATED  ENERGY,  (b)  CAUSES  OF  SPEECH  DISTORTION — 
"ELECTRICAL  INERTIA";  RECEIVER  DISTORTION;  TRANSMIT- 
TER DISTORTION.  (c)  NON-LINEAR  AMPLIFICATION  AND 
SPEECH  DISTORTION;  TYPES  OF  DISTORTION,  (d)  SECRECY 
OF  COMMUNICATION  IN  RADIO  TELEPHONY,  (e)  STRAY 
INTERFERENCE  IN  RADIO  TELEPHONY;  "TRANSMISSION  FAC- 
TOR OF  SAFETY";  "ASSISTANCE  OF  CONTEXT." 

1.  WORLD  ASPECTS. 

Before  presenting  to  our  readers  the  technical  details  of  radio  tele- 
phony, we  shall  discuss  briefly  the  effects  of  this  new  type  of  communica- 
tion on  international  affairs  and  world  growth. 

It  is  most  difficult  for  a  citizen  of  a  modern  state,  beside  whose  break- 
fast table  lies  the  printed  sheet  bearing  the  most  recent  news  of  widely 
distant  happenings,  to  realize  the  elaborate  and  delicately  adjusted 
mechanism  which  makes  the  entire  earth  his  mental  neighborhood.  The 
labor  of  gathering  accurate  news,  the  transfer  of  these  to  the  telegraph  or 
telephone  lines,  the  transmission  of  these  across  ocean  or  continent  by 
the  highly  evolved  radio  telegraph  or  cable,  and  the  huge  task  of  editing, 
printing,  and  distributing  them:  all  this  shows  but  dimly  in  the  final 
result.  And  yet,  possibly  the  most  fundamental  difference  between  sav- 
agery and  civilization  and  the  most  potent  source  of  the  latter  is  com- 
munication. The  isolation  of  any  modern  state,  the  communication  lines 
of  which  were  irretrievably  broken,  would  be  truly  tragic.  The  ties  that 
would  be  broken  would  be  not  merely  financial  but  in  every  field  of 
human  endeavor.  Imagine  a  state  which  heard  nothing  of  the  politics, 


2  Persona!  Aspects  of  Radio  Telephony 

art,  science,  and  literature  of  all  the  others.  Picture  the  provincialism, 
the  backward  and  undeveloped  craving  for  the  beautiful  in  art,  the  lack 
of  co-ordinated  scientific  research  and  industrial  development  dependent 
thereon,  and  the  childish  literature  which  would  result.  A  second  ' '  Dark 
Ages"  of  the  mind  and  spirit  would  follow;  and  the  citizens  of  the 
segregated  state  would  be  willing  to  pay  almost  any  price  for  the  restora- 
tion of  communication.  The  evil  effects  of  lack  of  communication  on 
commerce  need  not  be  dwelt  on ;  their  magnitude  and  inevitability  partake 
of  the  obvious.  Commerce  finds  itself  equally  dependent  upon  rapid  and 
reliable  communication.  It  is  exceptional  that  money  in  the  form  of  the 
actual  gold  or  silver  is  physically  transferred  from  one  country  to 
another  to  settle  debts.  Payment  is  made  by  the  transfer  of  credits 
between  the  countries  or  their  merchants,  and  this  transfer  requires 
nothing  more  than  the  use  of  the  radio  or  cable  station  for  a  few  minutes. 
Only  the  small  outstanding  monthly  or  annual  balance  in  favor  of  one 
or  the  other  is  physically  conveyed  between  the  merchants,  and  even 
this  but  rarely. 

2.  PERSONAL  ASPECTS. 

Aside  from  these  larger  aspects  of  communication,  there  are  other 
advantages  of  communication  which  are  priceless  to  the  individual.  The 
most  obvious  of  these  is  the  call  for  help  in  time  of  peril.  We  cannot 
gauge  the  value  of  a  radio  station  on  ship-board  to  the  passenger  or 
crew  after  collision  or  the  breaking  out  of  fire.  The  stringent  laws  of 
all  nations  relative  to  ship  sets  speak  clearly  for  the  opinion  of  the 
world.  And  marine  law  (and  even  naval  law)  have  been  altered  by 
requiring  the  captain  of  the  ship  to  remain  directly  and  immediately 
responsible  to  his  superiors  on  shore. 

Modern  business  would,  of  cour.v.  bis  helpless  except  for  the  tele- 
graph and  telephone.  Imagine  our  great  companies  in  a  world  where 
all  communication  was  by  word  of  mouth,  or  by  letter!  The  wheels 
of  industry  would  turn  but  slowly  when  weighted  down  and  clogged 
by  slow  and  unreliable  communication. 

In  the  more  personal  matters  of  life,  the  literal  extension  of  the 
personality  by  the  telephone  constitutes  an  inestimable  privilege.  The 
more  pleasant  social  amenities  become  possible  to  all.  Mere  distance 
need  no  longer  correspond  to  isolation,  for,  in  effect,  distance  is  com- 
pletely bridged. 

To  summarize:  in  its  larger  aspects,  COMMUNICATION  is  THE  LIFE- 
BLOOD  OF  CIVILIZATION,  OF  INTERNATIONAL  GOOD  WILL,  AND  OF  PROGRESS. 

To  the  individual,  IT  is  AT  ONCE  THE  CLIMAX  OF  CONVENIENCE  AND 

THE  ULTIMATE  EXTENSION  OF  PERSONALITY  IN  TIME  AND  SPACE. 


Uses  of  Radio  Telephony  3 

3.  USES  OF  RADIO  TELEPHONY. 

(a)  The  most  natural  use  of  radio  telephony  is  from  ship  to  ship  and 
from  ship  to  shore.    Since  it  is  the  only  means  of  telephonic  communica- 
tion  possible   under   the   circumstances,   it    does   not   need   to   compete 
with  wire  telephones  or  cables.     By  the  use  of  amplifying  relays  at 
the  receiving  end   (on  shore),  it  will  be  possible  to  enable  any  person 
on  the  ship  to  communicate  directly  with  persons  on  land,  in  part  over 
the  regular  wire  lines  and  in  part  by  radio.     The  details  of  such  com- 
munication will  be  explained  in  connection  with  "Radiophone  Traffic.'* 
The  great  advantage  of  radio  telephony  over  radio  telegraphy  on  board 
ships  is  the  direct  personal  contact  between  the  persons  corresponding 
and  the  resulting  possibility  of  speedily  settling  the  matters  at  issue^ 
and  (e.g.,  on  freighters  or  tramp  steamers)  the  freedom  from  the  neces- 
sity of  understanding  the  code.    Of  course,  this  last  advantage  is  bound 
up  with  the  simplification  of  ship  radio  telephone  sets  to  the  point  where 
a  skilled  operator  becomes  unnecessary,  the  manipulation  being  simple 
and  certain. 

(b)  A  second  important  field  for  radio  telephony  is  in  trans-oceanic 
and  trans-continental  work.     In  the  first  of  these,  radio  telephony  is 
unique  in  meeting  the  requirements  and  is  free  from  competition  with 
submarine  telephone  cables.     In  the  latter  case,  it  would  have  to  meet 
the   competition  of  the  long  distance  telephone  lines.     In   each  ease- 
communication    between    Subscriber    A    and    Subscriber   B    would   be 
through  their  wire  lines  to  the  nearest  radio  telephone  high  power  station 
and  thence  automatically  re-transmitted  through  an  amplifying  relay. 
This  will  be  further  explained  in  a  later  chapter. 

(c)  There  are  certain  types  of  regions  where  radio  communication  is 
the  only  one  possible  of  maintenance,  e.g.,  in  the  arctic  regions  (because  of 
snow  and  ice  interference  with  wire  lines),  in  densely  wooded  tropical 
regions  (because  of  the  enormous  difficulty  of  maintaining  a  clear  right 
of  way  through  rapidly  growing  and  luxuriant  vegetation),  in  regions 
or  across  regions  occupied  in  part  by  hostile  savage  tribes    (who  are 
addicted  to  the  use  of  copper  telegraph  wire  for  ornament),  and  between 
islands   and  the   mainland    (where   precipitous  rocky   coasts  or   swift 
currents  injure  or  sweep  away  cables).     In  all  of  these  cases,  radio 
telephony  offers  its  usual  advantages  and  will  no  doubt  come  into  increas- 
ing use. 

(d)  Between  two  moving  trains  or  between  moving  trains  and  fixed 
land  stations.     Here,  too,  we  are  practically  restricted  to  radio  communi- 
cation.   The  obvious  advantages  of  such  installations  in  times  of  storm,, 
when  wire  lines  are  almost  always  incapacitated,  has  been  shown  by  the 
experiences  of  the  officials  of  the  Delaware,  Lackawanna  &  Western 
Railroad  in  times  of  blizzards.     They  have  kept  in  touch  with  their 


4  Special  Applications 

otherwise  marooned  trains,  and  have  greatly  simplified  the  problem 
of  resuming  normal  traffic  schedules.  And  even  in  fair  weather,  the 
advantage  of  keeping  all  trains  in  touch  with  each  other  and  the  control 
of  train  dispatching  is  obvious.  Occasional  failures  of  the  block  system 


-  DISTANCE    OF    TRANSMISSION  - 
FIGURE  1 — Comparison  of  cost;   radio  vs.  wire  telephony. 


become  far  less  dangerous,  because  it  is  possible  to  warn  a  train  regard- 
less of  its  position  relative  to  the  signals.  In  foggy  weather,  this  accurate 
moment-to-moment  information  as  to  train  positions  is  far  from  being 
a  drawback  to  the  normally  anxious  passenger  on  certain  railroads. 

(e)   There  are  a  number  of  special  applications  of  radio  telephony 
which  have  not  as  yet  been  developed  to  the  point  at  which  it  is  possible  to 


Overland  Radio  vs.  Wire  Telephony  5 

make  any  very  definite  statement  as  to  their  ultimate  value.  Among  these 
are  telephonic  communication  between  various  levels  of  a  mine  and  the 
surface  (which  communication  would  greatly  increase  the  chance  of  an 
early  rescue  in  cases  of  cave-in,  where  wire  lines  are  almost  always 
broken),  communication  between  government  foresters,  communication 
between  aeroplanes  or  dirigibles  and  the  ground,  and  communication 
between  submarines  and  ship  or  shore. 

4.  RADIO  VERSUS  WIRE  TELEPHONY. 

It  is  very  difficult,  if  not  impossible,  to  institute  a  fair  comparison 
between  these  fields  at  the  present  time.  Radio  telephony  is  so  far 
from  having  reached  an  advanced  stage  of  development,  and  is  so 
seriously  threatened  on  the  research  side  by  government  control  and 
naval  or  postal  administration,  that  our  conclusions  are  little  better 
than  guesses.  However,  certain  broad  considerations  are  fairly  obvious 
and  probable. 

Let  us  consider  Figure  1.  Horizontally  we  have  laid  off  on  an 
arbitrary  scale  the  distance  over  which  telephone  transmission  is  being 
carried  on,  the  extreme  distance  covered  by  the  chart  being  probably  of 
the  order  of  magnitude  of  2,000  miles.  Vertically,  the  cost  for  a  three- 
minute  toll  message  has  been  laid  off,  the  extreme  cost  indicated  being  of 
the  rough  order  of  magnitude  of  $15  for  three  minutes.  It  is  understood 
that  these  values  may  easily  be  as  much  as  fifty  per  cent,  or  more  in  error. 

(a)  LAND  TELEPHONY. 

For  short  distances,  there  seems  to  be  no  question  as  to  the  super- 
iority of  wire  transmission.  The  difficulty  of  preventing  interference 
between  a  multiplicity  of  radio  telephone  stations,  the  first  cost  of  even 
a  low  power  radiophone  station,  the  first  cost  of  the  transmitting  and 
receiving  antennas  and  ground,  and  the  occasional  skilled  attendance 
required  (at  least,  by  present-day  radiophones)  render  the  idea  of  replac- 
ing the  complex  network  of  a  city's  wire  telephone  system  by  radio- 
phones highly  improbable.  This  feature  is  clearly  shown  by  the  lower 
portions  of  the  fine  line  curves  of  Figure  1,  wherein  the  influence  of 
first  cost  on  transmission  over  wire  telephones  and  radiophones  is 
qualitatively  shown.  There  may  be  occasional  exceptions  to  the  curves 
shown ;  for  example,  in  the  case  of  very  special  types  of  service.  Thus, 
it  might  be  desirable  for  a  military  or  police  force  to  maintain  radio- 
phonic  rather  than  wire  line  communication,  for  obvious  reasons.  But 
except  when  such  special  circumstances  render  radio  communication 
imperative,  the  radiophone  would  seem  to  be  at  a  disadvantage  for  short- 
range  communication.  As  we  gradually  increase  the  range  of  com- 


6  Oversea  Radio  vs.  Cable  Telephony 

munication,  the  circumstances  may,  however,  alter.  The  vast  expense 
of  maintaining  a  two  or  three  thousand  mile  long  wire  line,  against 
sleet  and  snow,  high  wind,  defective  insulation,  casual  depredation,  (and 
sometimes  over-luxuriant  vegetation)  then  come  into  consideration.  If 
the  wire  line  crosses  one  or  more  mountain  chains,  there  are  bound  to 
be  troublesome  and  weak  points.  Underground  cables  for  wire  telephony, 
except  in  the  case  of  very  high-grade  and  comparatively  short-distance 
traffic,  have  not  come  into  use  because  of  their  great  cost.  In  addition, 
long  telephone  lines  must  be  "loaded"  electrically  to  prevent  excessive 
speech  distortion,  and;  require  the  use  of  fairly  elaborate  two-way 
amplifiers  at  a  number  of  points  along  the  line.  When  it  is  considered 
that  the  cost  of  the  line  alone  in  the  New  York-San  Francisco  wire  tele- 
phone transmission  is  in  the  neighborhood  of  two  million  dollars,  and 
that  this  line  must  be  constantly  patrolled  by  hundreds  of  men,  it  will 
be  seen  that  radio  telephony  may  well  come  into  consideration.  That 
is  to  say,  at  some  point  (e.g.,  X  in  Figure  1),  the  radiophone  may  be- 
come more  desirable  than  the  wire  telephone.  There  is  no  question  that 
the  distance  of  transmission  corresponding  to  this  point  X  depends 
directly  on  the  extent  to  which  strays  can  be  eliminated  in  reception. 
It  may  safely  be  said  that  so  long  as  radio  telephony  over  long  distances 
is  dependent  on  absence  of  serious  atmospheric  disturbances,  it  will  be 
handicapped  thereby.  With  the  advent-  of  apparatus  which  markedly 
reduces  stray  intensity,  wire  line  telephony  over  very  considerable  dis- 
tances will  be  at  a  marked  disadvantage.  This  will  result  in  shifting  the 
point  X  far  to  the  left  of  the  position  indicated  in  Figure  1. 

(b)  OVERSEA  TELEPHONY. 

As  soon  as  we  consider  telephony  over  water,  we  find  a  different 
state  of  affairs  existing.  It  is  questionable  whether  radio  is  not  always 
less  expensive  than  cable  telephony  in  this  case.  Certain  it  is  that  over 
great  stretches  of  water,  radio  telephony  is  at  an  enormous  advantage 
because  of  the  great  cost  of  laying  and  maintaining  the  type  of  cable 
required  for  submarine  telephony  and  also  because  radio  communication 
over  water  is  always  accomplished  with  less  power  than  for  the  equal 
distance  over  land.  Consequently,  we  have  tentatively  indicated  in 
Figure  1  the  sea  radio  telephony  curve  as  lying  below  the  sea  cable  tele- 
phony curve  throughout  the  length  of  each,  and  with  the  advantage  of  the 
former  becoming  specially  marked  for  great  distances.  Of  course,  so 
far  as  long  range  oversea  communication  with  ships  is  concerned,  the 
radiophone  has  no  rival. 

Passing  now  to  the  technical  aspects  of  radio  telephony,  we  desire 
to  make  clear  the  scope  of  this  book.  It  is  not  in  the  least  intended 
to  give  every  practical  detail  of  construction  of  a  "50  mile  radiophone 


Broad  Problems  Involved  in  Radio  Telephony  7 

set/'  or  indeed  to  go  into  many  practical  details  of  construction  at  all. 
The  reason  for  this  is  two-fold.  First  of  all,  the  limitations  of  space 
would  prevent  adequately  treating  all  existing  methods  of  radio  tele- 
phony, even  were  all  data  available,  and  secondly,  the  cost  to-day  of 
building  a  reliably  operative  radiophone  over  any  considerable  distance 
is  beyond  the  reach  of  most  experimenters.  In  other  words,  the  average 
amateur  might  just  as  well  not  attempt  to  construct  such  sets  in  the 
present  state  of  the  art.  Furthermore,  it  is  not  possible  for  us  here 


FIGURE  2 — Oscillogram  of  vowel  sounds   "ah." 

to  give  due  credit  to  all  those  responsible  for  the  historical  development 
of  each  device  described ;  nor  to  assign  with  any  certainty  patent  rights 
in  the  apparatus  mentioned.  Present-day  litigation  and  confusion  as 
to  patent  rights  would  render  such  a  course  inappropriate  on  our  part. 
We  cannot  even  cover  the  entire  field  of  radio  telephony  exhaustively. 
At  best,  we  can  only  describe  certain  interesting  and  operative  methods 
of  radio  telephony,  assigning  them  to  the  manufacturer  or  designing 
engineer  at  present  concerned  with  them,  and  giving  proposed  changes 
or  improvements. 

5.  BROAD  PROBLEMS  INVOLVED  IN  RADIO  TELEPHONY. 

These  problems  are  the  following:  (a)  that  of  radiating  energy  at 
all  for  this  purpose;  (b)  distortion  of  speech  due  to  several  causes;  (c) 
the  allied  problem  of  amplification  of  speech  at  transmitter  and  receiver 
without  distortion;  (d)  the  obtaining  of  secrecy,  and  (e)  the  reduction 
of  stray  disturbances. 

(a)     RADIATION    OF  MODULATED   ENERGY. 

It  first  becomes  incumbent  on  us  to  consider  the  nature  of  speech. 
In  the  back  of  the  throat  of  the  speaker  a  sort  of  membrane  known  as 
the  "vocal  cords"  is  set  into  more  or  less  continuous  vibration  by  the 
breath.  The  quality  of  the  resulting  sound  is  modified  in  at  least  two 


8  Nature  of  Speech;  Audio  Telephony 

ways:  by  altering  the  shape  of  the  mouth  with  the  tongue  or  otherwise 
and  thus  causing  a  degree  of  selective  resonance,  and  by  actually  starting 
or  stopping  the  stream  of  sound  as  is  done  with  the  harsher  consonants, 
e.g.,  the  letter  "d."  The  extreme  complexity  of  the  resultant  sound 
vibration  of  the  air  is  illustrated  in  the  oscillogram  of  Figure  2.*  This 
is  a  record  of  the  current  in  a  telephone  line  (and  therefore  approxi- 
mately of  the  sound  in  the  receiver)  corresponding  to  the  sustained 
vowel  sound  "ah"  (as  in  "bah"),  a  clear-speaking  man's  voice  being 
used  for  the  test.  The  total  time  of  the  record  is  slightly  over  one- 
twentieth  of  a  second.  The  basic  vibration  was  of  approximate  frequency 
of  800  cycles  per  second  and  the  chief  modification  thereof  occurs  with  a 
frequency  of  120  cycles  per  second.  The  great  complexity  of  speech,  even 
for  the  comparatively  regular  vowel  sounds,  is  well  illustrated.  When 
the  comparative  crudity  of  radio  telegraphy  is  considered,  the  difficulty 
of  radio  telephony  becomes  obvious.  On  the  one  hand,  in  telegraphy 
as  nearly  as  possible  complete  and  abrupt  starting  and  stopping  of  the 
energy  flow  is  required  and  this  at  no  very  rapid  rate.  In  radio  tele- 
phony, on  the  other  hand,  the  outgoing  flow  of  energy  must  be  moulded 
and  modulated  with  close  approximation  to  the  excessively  complicated 
wave  form  of  the  speech  vibrations.  The  difference  in  degree  is  not  far 
from  that  between  ruling  a  dot-and-dash  line  and  making  a  dry-point 
etching  of  an  autumn  landscape. 

Given,  then,  the  complex  vibrations  which  constitute  speech,  the  prob- 
lem of  radiating  the  moulded  energy  arises.  Of  course,  on  a  small  and 
feeble  scale  the  problem  is  solved  in  every-day  conversation  between  two 
persons.  This  may  be  termed  a  species  of  "audio  telephony,"  the  fre- 
quency of  the  radiated  air  waves  being  those  of  the  speech  itself,  i.  e., 
of  the  order  of  800  cycles  per  second.  The  same  sort  of  solution 
might  be  attempted,  using  the  electromagnetic  "ether"  waves  of  audio 
(i.  e.f  audible)  frequency  to  carry  the  telephone  message.  This  solu- 
tion is  entirely  unsatisfactory  for  a  number  of  reasons.  Firstly,  the 
•  frequencies  in  speech  vary  considerably,  and  the  radiating  system  (an- 
tenna) could  not  remain  resonant  to  all  these  frequencies  and  their 
corresponding  electromagnetic  wave  lengths.  Secondly,  the  wave  length 
would  be  excessively  long,  being  375,000  meters,  or  230  miles,  for  the 
frequency  of  800  cycles  per  second.  This  would  require,  for  fairly 
effective  radiation,  an  antenna  of  the  length  of  say  10  to  20  miles,  which 
is  beyond  the  dreams  of  even  the  designers  of  the  highest  powered  sta- 
tions. Were  an  ordinary  antenna  about  300  feet  (100  meters)  high 
to  be  used,  its  radiation  resistance  at  800  cycles  would  be  0.0001  ohm, 
necessitating  an  antenna  current  of  no  less  than  3,000  amperes  to  radiate 
even  1  kilowatt  effectively.  It  is  unpleasant  to  imagine  the  voltage  at 

*  This  unusually-  clear   record  the  Author  owes  to  the  kindness  of  Mr.  John  B.  Taylor. 


Nature  of  Speech 


the  antenna  top  under  these  conditions;  its  value  being  not  far  from 
a  million  volts.  Obviously,  as  a  practical  consideration,  radio  telephony 
by  means  of  electromagnetic  waves  of  the  same  frequency  as  that  of 
speech  vibrations  is  out  of  the  question. 

At  this  point  the  problem  of  radio  telephony  looks  sufficiently  hope- 
less; but  fortunately  an  ingenious  alternative  (and  a  successful  one)  is 
available.  Let  the  rippling  curve  of  Figure  3  represent  the  sound  vibra- 
tions corresponding  to  some  spoken  word.  If  this  word  was  recorded  on 
a  vertical-cut  phonograph  record,  a  cross  section  of  the  groove  of  the 


FIGURE  3 — Typical  wave-form. 

record  would  show  this  curve  as  indicated.  If  a  needle,  indicated  in 
the  figure,  were  to  move  from  left  to  right  along  the  groove,  and  were 
pressed  against  the  record  it  would  also  move  up  and  down.  If  a  dia- 
phragm were  fastened  -to  the  upper  end  of  the  needle,  this  diaphragm 
would  set  into  motion  the  air  near  it,  and  the  resulting  sound  vibrations 
would  be  an  accurate  reproduction  of  the  original  speech  used  in  making 
the  record.  So  far,  we  are  on  familiar  enough  ground. 


f\ 


A    |  "RflCMO    FREQUENCY 

FIGURE    4— Basis    of    radio   telephony    by    audio 
frequency   modulation  of  radio  frequency  energy. 


10      Audio  Frequency  Modulation  of  Radio  Frequency  Energy 

But  suppose  that  we  were  suddenly  to  encounter  a  difficulty  of  the 
following  kind:  Imagine  that  it  were  not  feasible  to  secure  a  large 
enough  diaphragm  at  the  top  of  the  needle  to  set  much  air  into  motion. 
We  might  choose  to  use  a  small  diaphragm  vibrating  very  rapidly  instead. 
In  fact,  we  might  arrange  that  this  diaphragm  vibrated  so  rapidly  that 
its  vibrations  could  not  be  heard  at  all,  but  only  the  variation  in  their 
amplitude  or  width  of  swing.  Our  phonograph  record  would  now  have 
to  assume  the  curious  appearance  of  the  thin-line  to-and-fro  curve  of 
Figure  4.  This  curve  has  been  appropriately  marked  * '  radio  frequency ' ' 
in  the  figure,  as  distinguished  from  the  heavy  or  envelope  curve  marked 
" audio  frequency."  The  audio  frequency  curve  is  exactly  the  same 
as  before,  but  it  is  replaced  for  radiating  purposes  by  the  moulded  or 
modulated  radio  frequency  curve.  The  radio  frequency  curve  should 
strictly  not  have  sharp  peaks  at  the  extreme  of  each  alternation  but 
should  be  a  rounded  "sine"  curve.  For  clearness  in  the  figure,  it  has 
been  indicated  as  sharply  peaked.  Its  frequency  must  be  over  10,000 
cycles  per  second,  corresponding  to  inaudible  "sound." 

It  may  seem  peculiar  to  speak  of  "hearing  the  variations  in  ampli- 
tude of  a  super-audible  vibration,"  yet  this  is  entirely  possible.  All  we 
should  need  under  the  simplest  conditions  would  be  a  "  sound  rectifier ' ' ; 
i.  e.,  a  device  which  permitted  only  one-half  of  the  radio  frequency  sound 
to  reach  the  ear.  This  would  correspond,  in  Figure  4,  to  admitting  to 
the  ear  only  those  portions  of  the  radio  frequency  vibration  which  lie 
above  the  middle  line.  Although  the  ear  could  not  follow  each  of  the 
myriad  radio  frequency  impulses  which  it  would  thus  receive,  neverthe- 
less the  ear  drum  would  receive  inward  pushes  of  an  amplitude  variation 
corresponding  to  the  heavy-line  audio  frequency  curve.  Consequently 
the  variations  in  the  super-audible  vibration  would  certainly  be  heard. 
The  necessity  for  the  ' '  sound  rectifier ' '  is  clear  enough  when  we  consider 
that  without  it  extremely  rapid  impulses  on  the  ear  drum  in  opposite 
directions  (corresponding  to  the  entire  radio  frequency  curve)  would 
.  merely  neutralize  each  other,  causing  no  actual  motion  of  the  heavy 
ear  drum.  It  is  assumed  that,  though  the  ear  drum  can  follow  audio  fre- 
quency vibrations  readily  enough,  its  inertia  is  so  great  that  it  could  not 
follow  the  radio  frequency  vibrations  to  any  appreciable  extent.  Hence 
the  necessity  for  the  "sound  rectifier"  producing  mono-directional  im- 
pulses of  varying  amplitude  instead  of  bi-directional  mutually  neutral- 
izing pushes-and-pulls  of  variable  amplitude. 

If  we  substitute  for  the  explanation  in  the  above  imaginary  acoustic 
case,  the  corresponding  electrical  case,  we  find  that  the  explanation  given 
holds  equally.  Since  our  antennas  are  too  small  electrically  to  radiate 
effectively  audio  frequency  electromagnetic  waves  (as  shown  in  an  earlier 
paragraph),  we  are  compelled  to  telephone  by  means  of  the  variation 


Receiving  Rectifier;  Wave  Length  Modulation  11 

of  super-audible  (that  is,  radio  frequency)  electromagnetic  waves.  In 
other  words,  the  energy  actually  radiated  from  the  station  must  resemble 
the  "radio  frequency"  curve  of  Figure  4,  and  follow  in  its  envelope 
curve  (i.e.  the  audio  frequency  curve)  the  original  sound  vibrations. 

The  necessity  for  the  crystal  or  valve  rectifier  (corresponding  to  the 
imaginary  "sound  rectifier"  mentioned)  is  also  evident  if  we  substitute 
in  the  analogy  already  given  the  combination  of  telephone  diaphragm 
and  ear  drum  for  the  ear  drum  itself.  Its  function  will  be  seen  to  be 
the  furnishing  of  mono-directional  mutually  assisting  electrical  impulses 
which  can  push  aside  a  heavy  telephone  diaphragm,  which  same  dia- 
phragm would  hardly  respond  at  all  to  the  bi-directional  mutually 
neutralizing  unrectified  impulses. 

From  the  foregoing,  we  can  draw  one  very  important  conclusion. 
The  radio  frequency  used  in  radio  telephony  must  be  quite  inaudible 
and  completely  steady,  a-nd  many  times  higher  than  the  audio  frequency 
voice  vibrations.  Otherwise  we  should  hear  in  the  receivers  a  continuous, 
high,  and  piercing  tone  corresponding  to  the  ever-present  radio  frequency, 
which  shrill  tone  would  naturally  be  an  objectionable  interference  with 
the  conversation.  Furthermore,  the  accurate  reproduction  of  the  deli- 
cate overtones  in  the  voice,  which  are  of  fairly  high  frequency  them- 
selves, is  dependent  on  having  many  radio  frequency  cycles  available 
for  the  moulding  process,  so  that  the  envelope  curve  will  be  very 
faithfully  followed. 

It  is  to  be  noted  that  a  second  method  of  radio  telephony  exists, 
which  might  be  termed  "modulation  by  change  of  frequency  (or  wave 
length)."  Instead  of  altering  the  amplitude  of  the  radiated  waves  in 
accordance  with  the  envelope  speech  curve,  we  might  systematically 
increase  and  diminish  the  radiated  frequency  in  proportion  to  the 
envelope  curve.  For  example,  while  normally  radiating  at  50,000  cycles 
per  second  (6,000  meters  wave  length),  we  might  alter  the  frequency  say 
to  48,000  cycles  at  points  corresponding  to  the  peaks  in  the  audio  fre- 
quency curve,  to  49,000  meters  for  points  corresponding  to  half-way 
between  peak  and  zero  in  the  audio  frequency  curve,  and  so  on.  At  the 
receiving  station,  the  response  in  the  detector  circuit  would  then  be 
proportional  (or  nearly  so)  to  the  speech  curve  in  view  of  the  tuning 
and  detuning  effects  which  would  occur  in  the  receiver  as  the  rapidly 
varying  frequency  was  received.  This  method  permits  keeping  appreci- 
ably full  load  on  the  radio  frequency  generator  at  all  times. 

It  is  the  view  of  the  writer  that  any  such  method  is  objectionable 
in  that  it  distributes  the  radiated  energy  over  a  considerable  range  of 
wave  lengths,  thereby  increasing  the  liability  to  interference  with  other 
stations.  Furthermore,  stray  reduction  will  probably  require  the  recep- 
tion of  a  single  sharply  defined  frequency. 


12  Causes  of  Speech  Distortion 

A  third  alternative  method  exists  for  radio  telephony,  this  being 
a  combination  of  the  first  two.  That  is,  both  the  amplitude  and  the 
frequency  of  the  radiated  waves  are  varied  in  accordance  with  the 
audio  frequency  curve.  This  method,  rather  than  the  second,  has 
been  occasionally  used ;  but  it  suffers  from  the  same  defects  as  the  second 
method  and  has  no  great  advantages  over  the  first. 

(b)    CAUSES    OF    SPEECH    DISTORTION    IN    RADIO    TELEPHONY. 

In  radio  telephony  we  are,  of  course,  vitally  concerned  in  preserving 
faithfully  the  exact  quality  of  speech  from  the  speaker  to  the  ear  of 
the  person  receiving  the  message.  That  is,  the  wave  form  of  the  original 
sound  (as  shown  in  Figure  3  and  also  in  the  dotted  outline  in  Figure  6) 
must  be  in  no  way  distorted  in  transmission  and  reception.  This  requires 
considerable  care  in  the  various  stages  of  the  process  of  radio  telephony, 
as  will  appear  -from  the  following  review  of  the  causes  of  distortion  and 
their  remedies. 

To  begin  with,  there  is  a  type  of  distortion  which  may  be  termed  ' '  fly 
wheel"  or  inertia  distortion.  It  arises  in  a  fashion  which  can  be  made 
clear  from  a  mechanical  analogy.  If  we  have  a  fly  wheel  in  rapid 
rotation,  there  is  a  marked  and  well-known  tendency  of  the  wheel  to 
maintain  a  constant  speed  because  of  the  large  amount  of  energy  stored 
in  its  rotating  mass.  If  we  attempt  to  change  the  speed  of  the  wheel 
very  greatly  in  an  exceedingly  brief  time,  we  shall  meet  with  almost  in- 
superable opposition.  The  "inertia  reaction"  of  the  wheel  will  be  very 
marked.  If,  on  the  other  hand,  we  attempt  to  change  the  speed  slightly 
in  a  considerable  longer  time,  we  shall  find  the  task  a  much  easier  one. 
In  other  words,  the  fly  wheel  resists,  markedly,  rapidly  recurrent  changes 
in  its  speed  of  rotation  but  permits,  fairly  well,  slow  changes  in  its  speed. 
Of  course,  the  same  effect  exists  with  any  mass.  If  we  attempt  to  start 
and  stop  a  heavily  loaded  freight  car  a  thousand  times  per  second,  huge 
forces  will  be  called  into  play  if  the  to-and-fro  swing  of  the  car  is 
appreciable.  If  we  attempt  to  start  and  stop  the  same  car  only  once 
per  second,  the  opposition  will  be  but  a  thousandth  as  great. 

The  application  of  this  principle  of  inertia  reaction  to  the  telephone 
transmitter  diaphragm  and  the  telephone  receiver  diaphragm  is  not 
far  to  seek.  It  is  clear  that  there  will  be  much  more  difficulty  in  getting 
the  telephone  diaphragm  to  respond  proportionately  to  the  higher  over- 
tones of  the  human  voice  than  to  the  lower  pitched  components.  This 
is  one  reason  why  a  high-pitched  voice  generally  fails  to  get  over  a 
telephone  line  with  complete  satisfaction  to  the  listener.  We  may  say, 
then,  that  the  telephone  transmitter  diaphragm  smooths  out  the  high 
overtones  of  the  voice,  with  the  result  that  crisp,  clear  enunciation  is  in 
part  lost.  The  obvious  remedy  is  to  have  light  transmitter  diaphragms 


Electrical  and  Mechanical  Inertia  Distortion  13 

without  much  pressure  on  them  from  the  carbon  grains  behind  the 
diaphragm.  We  are  much  limited  in  the  design  of  a  transmitter  by  other 
considerations,  so  that  it  is  generally  necessary  to  use  the  normal  trans- 
mitter. As  regards  the  receiver  diaphragm,  there  have  been  made  a 
number  of  attempts  to  use  thin  small  sheets  for  this  purpose,  and  it  has 
been  noted  that  they  respond  much  more  readily  to  the  present-day 
500-cycle  spark  signals  than  did  the  older,  heavier  diaphragm  receivers. 
On  the  other  hand,  it  is  desirable  to  avoid  receivers  in  which  the  dia- 
phragm is  markedly  resonant  to  any  frequency  within  the  normal  range 
of  speech,  else  this  frequency  wall  be  relatively  exaggerated  out  of  all 
proportion  to  its  actual  magnitude.  The  result  will  be  an  extremely 
annoying  "howling"  whenever  the  resonant  frequency  occurs  in  the 
speech. 

There  is  another  possibility  of  a  sort  of  "inertia"  distortion  due 
to  the  fact  that  the  radio  frequency  generator  (arc,  bulb,  alternator, 
etc.)  will  not  supply  sudden  violent  changes  in  output.  Consequently,  a 
similar  smoothing  down  of  the  higher  overtones  will  occur  unless  the 
radio  frequency  generator  is  without  "electrical  inertia"  (that  is,  has 
small  inductance)  and  also  is  operated  by  a  powerful  generator. 

It  is  well  at  this  point  to  indicate  clearly  what  is  meant  by  "elec- 
trical inertia. ' '  The  behavior  of  an  ordinary  inductance  when  an  alter- 
nating electromotive  force  (voltage)  of  various  frequencies  is  applied  at 
its  terminals  is  as  follows:  The  current  which  passes  through  the 
inductance  is  inversely  proportional  to  the  frequency ;  that  is,  the  in- 
ductance acts  like  an  electrical  mass  and  does  not  permit  the  ready 
passage  through  it  of  the  higher  frequency  currents.  It  is  to  be  noted 
further  that  the  effect  of  a  capacity  is  exactly  the  opposite  in  that  it 
exaggerates  the  passage  of  currents  of  higher  frequency  while  relatively 
retarding  those  of  lower  frequency.  This  is  the  basis  of  ordinary  tuning, 
which  is  nothing  more  than  balancing  the  choking  action  of  an  inductance 
at  a  given  frequency  by  the  opposite  effect  of  a  capacity. 

It  is  clear  enough  then  that  high  inductance  in  any  of  the  circuits 
in  which  speech  currents  flow  will  produce  an  objectionable  smoothing 
out  of  the  overtones  in  speech  so  that  the  speech  will  become  ' '  drummy ' ' 
through  the  exaggeration  of  the  basic  tones.  An  excess  of  capacity  in 
any  "speech  circuit  will  exaggerate  the  overtones,  and  the  speech  will 
become  "squeaky."  A  little  practice  in  telephony  soon  enables  the 
skilled  observer  to  tell  which  type  of  distortion  he  is  getting. 

A  smoothing-out  effect,  causing  drummy  speech,  is  also  obtained 
when  a  highly  persistent  antenna  is  coupled  to  the  sustained  wave 
generator  or  when  a  highly  persistent  receiver  secondary  is  coupled  to 
the  antenna.  This  is  due  to  the  fact,  first  shown  by  Bjerknes,  that  with 
loose  coupling  a  persistent  secondary  will  not  follow  the  sudden  varia- 


14  Transmitter  Distortion 

tions  in  the  primary  oscillations  except  with  a  time  lag  and  diminution 
in  the  abruptness  of  change.  It  is  this  effect  which  has  led  Poulsen  and 
others  to  use  entirely  aperiodic  secondaries  in  their  radiophone  receiving 
sets.  In  this  way,  the  persistency  distortion  in  coupling  is  avoided, 
though  at  the  cost  of  loudness  of  signal  and  selectivity,  i.  e.,  freedom 
from  interference  from  other  stations.  These  matters  will  be  further 
considered  under  receiver  design. 

A  fairly  prolific  source  of  speech  distortion,  or  rather  speech  des- 
truction, is  that  curiously  imperfect  instrument,  the  carbon  microphone 
as  used  in  the  ordinary  telephone  transmitter.  This  has  been  shown 
by  de  Forest,  who  states  that  when  speech  from  an  ordinary  transmitter 
is  very  greatly  amplified,  it  is  found  to  be  fairly  teeming  with  crackling 
and  hissing  sounds  caused  by  small  local  arcs  or  mechanical  disturbance 
effects  in  the  microphone.  This  is  not  astonishing  when  the  nature  of  the 
variable-resistance  carbon  contact  is  considered.  The  alternative  sug- 
gested by  de  Forest,  namely  the  use  of  an  ordinary  Bell  receiver  as  a 
transmitter  of  the  induction  type  is  feasible  only  if  one  is  willing  to 
amplify  greatly  the  extremely  small  output  of  such  a  transmitter.  On 
the  whole,  the  investigator  will  in  general  be  bound  to  use  carbon  trans- 
mitters with  small  currents  so  as  to  avoid  ''packing,"  hissing,  and  other 
disturbances. 

If  iron  cores  are  used  in  the  coils  of  transmitting  circuit  (e.  g.,  in 
magnetic  amplifiers,  or  speech-controlled  frequency  doublers),  a  further 
distortion  will  arise  because  of  the  * '  saturation ' '  effect  in  the  iron.  That 


FIGURE   5— Oscillogram   showing   distortion   when   range   of   linear 
proportionality  is  exceeded. 

is,  iron  core  coils  do  not  have  a  constant  inductance  at  all,  and  the  change 
in  their  inductance  is  particularly  marked  when  heavy  currents  are 
passed  through  the  coils  thus  saturating  the  iron.  An  interesting  example 
of  the  distortion  produced  in  a  magnetic  amplifier  is  taken  from  Mr.  E.  F. 


Non-linear  Distortion 


15 


W.  Alexanderson 's  paper  in  the  April,  1916  "Proceedings  of  the  Institute 
of  Radio  Engineers."  The  lower  curve  of  this  figure  shows  an  oscillo- 
gram  of  the  current  (amplified  speech  current)  passing  into  the  magnetic 
controlling  amplifier.  The  upper  curve  shows  resulting  voltage  of  the 
controlled  radio  frequency  alternator.  The  distortion  is  seen  to  occur 
between  points  X  and  Y  (corresponding  to  A  and  B  in  the  lower  curve) 
but  not  between  points  T  and  Z  (corresponding  to  B  and  C  in  the  lower 
curve).  That  is,  the  distortion  occurs  for  the  high  current  values  in  the 
iron-core  amplifier  control  winding  between  A  and  B.  Of  course,  such 
effects  are  avoided  by  working  the  iron  on  low  field  density  so  that  the 
flux  is  at  all  times  proportional  to  the  magnetizing  current  and  the  control 
range  is  not  exceeded.  This  can  be  accomplished,  though  sometimes  at 
the  cost  of  great  amplification  and  large  output. 

It  will  be  noticed  that  in  discussing  the  saturated-iron  distortion,  we 
have  encountered  a  case  of  non-linear  amplification,  and  resulting  dis- 
tortion. Non-linearity  of  amplification  is  sufficiently  common  and  im- 
portant to  warrant  detailed  consideration. 

(c)  NON-LINEAR  AMPLIFICATION  AND  SPEECH  DISTORTION. 

Let  us  consider  again  an  ordinary  phonograph  record  of  speech, 
and  let  us  suppose  that  the  record  in  question  is  to  be  " amplified" 


•HNflCCURflTE 


FIGURE  6— Non-linear  distortion. 


mechanically.  That  is,  we  wish  to  produce  a  record  similar  in  all 
respects  except  that  the  up-and-down  ripples  in  the  groove  are  to  be 
accurately  magnified  to  a  definite  extent  in  their  vertical  dimension  but 
their  length  is  to  remain  unchanged.  Such  a  record  would  produce 


16 


Linear  Amplification 


a  sound  of  much  greater  loudness  but  with  the  pitch  or  frequency 
unchanged.  (We  are  here  referring  to  a  vertical  cut  record,  of  the 
cylinder  type.)  This  amplifying  procedure  would  be  quite  satisfactory 
if  the  mechanism  that  cut  the  new  record  always  followed  the  original 
record  accurately,  and  faithfully  multiplied  every  vertical  dimension 
by  the  same  amount  Then,  in  Figure  6,  the  new  record  would  have  the 
cross-section  of  the  dotted  line  in  the  figure.  If,  however,  the  amplifying 
mechanism  magnified  accurately  only  for  displacements  near  the  axial 
line  but  responded  disproportionately  feebly  for  portions  of  the  curve 
lying  at  considerable  distances  from  the  axial  line,  we  should  get  the 
type  of  distortion  shown  in  the  full  line  of  Figure  6.  It  will  be  seen 
that  the  overtones  are  blurred  at  the  upper  portion  of  the  curve,  Avhich 
is  accordingly  labeled  ' '  inaccurate. ' '  In  the  lower  portion  of  the  curve, 
where  linear  proportionality  is  obtained,  the  curve  remains  accurate. 
The  whole  matter  is  shown  in  a  different  way  in  the  right  hand  diagram 
of  Figure  6,  where  input  of  the  amplifier  or  "excitation"  is  plotted 


FIGURE  7 — Non-linear  distortion. 


horizontally  against  output  or  "response"  vertically.  It  will  be  seen 
that,  for  the  accurate  portion  of  the  wave,  the  response-excitation  curve 
is  a  straight  line,  hence  the  name  "linear  amplification."  Up  further  it 
(flattens  out,  somewhat  like  an  iron  saturation  curve  and  it  is  here  that 
the  distortion  occurs.  Speech  of  this  type  would  generally  be  called 
"drummy." 


Speech  Distortion 


17 


In  Figure  7,  the  reverse  type  of  error,  leading  to  what  is  usually 
termed  "squeaky"  speech,  is  pictured.  It  will  be  seen  that  the  amplifi- 
cation is  linear  for  low  excitations,  and  that  consequently  the  lower 
portions  of  the  wave  near  the  axial  line  will  be  accurately  amplified. 
On  the  other  hand,  the  greater  excitations  produce  a  disproportionately 
great  response,  and  the  overtones  are  exaggerated- near  the  peak  of  the 
wave.  The  result  is  a  high  tinny  quality  to  the  speech. 

In  Figure  8  is  shown  a  sort  of  combination  effect  of  these  two,  which 
is  not  uncommon.  It  consists  of  a  disproportionately  feeble  response 
for  small  excitations,  a  proportional  response  for  moderate  excitations, 
and  a  disproportionately  feeble  response  for  great  excitations.  The  re- 
sulting wave  is,  as  will  be  seen,  accurate  only  for  moderate  values,  but 
flattened  as  to  overtones  near  the  axis  and  far  from  the  axis.  This  would 
be  badly  blurred  or  "muffled"  speech. 


EXCITflTlQN 


FIGURE  8 — Complex  non-linear  distortion. 

It  is  quite  clear  that  we  should  use  linear  control  systems  in  the 
liophone  transmitter  and  linear  amplifying  systems  in  the  radiophone 
ieiver.     With  the  magnetic  amplifier  for  transmission,  this  implies 
lower  iron  field-densities,   and  with  the  audion  receiving  amplifier  it 
iplies  working  below  the  saturation  current  point. 

(d)  SECRECY  OF  COMMUNICATION  IN  RADIO   TELEPHONY. 

If  a  frank  expert  were  to  be  asked  whether  "complete"  secrecy 
>uld  be  obtained  now  with  radio  telephony,  he  would  be  compelled  to 


18  Secrecy  in  Radio  Telephony 

answer  in  the  negative.  If  he  were  of  a  cynical  turn  of  mind,  he  might 
add  that  secrecy  was  no  more  obtainable  in  radio  telephony  now  than  in 
wire  telephony  or  any  other  form  of  communication,  a  remark  which 
recent  revelations  as  to  the  comparative  prevalence  of  official  "wire- 
tapping" would  more  than  justify.  Of  course,  any  wire  telephone  line 
can  be  tapped,  and  with  remarkable  ease  under  most  conditions.  At  one 
time,  the  telephone  companies  judged  it  necessary  to  maintain  wire 
communication  from  New  York  to  Boston  over  one  line  and  return  com- 
munication from  Boston  to  New  York  over  another  line  traversing  an 
entirely  different  route  from  the  first.  In  this  way,  even  the  adroit 
interloper  would  hardly  be  likely  to  tap  more  than  half  a  conversation. 
As  a  matter  of  fact,  the  drastic  expedient  suggested  was  not  adopted 
since  it  was  unnecessary  then  and  will  probably  continue  to  be  so.  A 
combination  of  severe  laws  against  tapping,  and  an  efficient  corps  of 
radio  inspectors  would  practically  solve  the  problem,  at  least  in  com- 
munities no  more  law-defying  than  those  of  the  United  States. 

As  an  illustration  of  the  ease  of  tapping  an  ordinary  (non-twisted, 
though  regularly  transposed)  telephone  line,  it  may  be  mentioned  that 
there  is  much  used  abroad  a  simple  secondary  coil,  which,  when  placed 
suitably  near  the  line,  picks  up  ordinary  conversation  without  any 
visible  physical  connection,  permanent  injury,  or  other  trace.  Even  the 
effect  on  the  transmission  would  be  practically  infinitesimal. 

It  is  to  be  expected,  on  the  other  hand,  that  when  radio  telephony 
becomes  commercial  and  widespread,  we  shall  have  stringent  laws  against 
"listening-in"  on  commercial  wave-lengths,  and  these  laws  will  be 
adequately  enforced.  By  the  use  of  a  number  of  modified  waves  or 
by  other  technical  methods  under  development  at  present,  unauthorized 
"listening-in"  will  become  exceedingly  difficult,  and  possible  of  attain- 
ment only  by  persons  of  expert  ability.  Such  persons,  however,  are 
easily  known  and  can  be  supervised  in  their  activities;  much  as  is  now 
the  case  with  excessively  skillful  engravers  of  bank  notes.  In  fact, 
systems  can  be  imagined  whereby  "listening-in"  would  be  futile  unless 
the  listener  had  a  code  combination  whereby  the  peculiar  material  sent 
could  be  automatically  re-converted  into  clear  speech.  This  indicates 
a  possibility  of  complete  secrecy. 

In  short,  while  secrecy  in  radio  telephony  involves  more  inspection 
than  for  wire  telephony,  it  can  be  brought  to  the  same  or  even  a  greater 
degree  of  certainty  by  technical  and  legal  measures. 

(e)  STRAY  INTERFERENCE  IN  RADIO  TELEPHONY. 

One  of  the  most  serious  outstanding  problems  in  radio  communica- 
tion is  the  elimination  of  atmospheric  disturbances  and  stray  electro- 


Stray  Interference  19 

magnetic  waves.  To  begin  with,  under  normal  summer  conditions, 
particularly  in  the  tropics,  the  effect  of  strays  is  practically  to  prevent 
stations  from  working  at  all,  part  of  the  time.  Aside  from  the  six-to-one 
to  ten-to-one  ratio  of  signal  strength  in  favor  of  winter  time,  the  strays 
complicate  the  problem  of  reliable  transmission  vastly.  As  a  result, 
most  radio  stations  work  with  a  "factor  of  danger"  rather  than  the 
normal  engineering  "factor  of  safety."  Whereas  an  engineer  will 
normally  design,  for  example,  a  bridge  so  as  to  stand  five  or  ten  times 
the  maximum  load  which  it  will  be  called  on  to  bear,  (that  is,  with  a 
factor  of  safety  of  ten),  the  radio  engineer  is  unable  to  guarantee  trans- 
mission over  great  distances,  particularly  in  the  tropics,  without  the  use 
of  excessive  and  commercially  unprofitable  amounts  of  power.  The 
result  is  that  a  compromise  is  always  made  between  absolutely  reliable 
service  (and  no  profits)  and  moderately  reliable  service  on  a  financially 
feasible  basis. 

If  however,  ninety  per  cent,  of  the  strays  could  be  eliminated  in 
reception,  the  effect  would  be  virtually  to  increase  by  ten  times  the 
power  of  every  transmitting  station  and  to  render  communication 
entirely  reliable  even  where  it  had  been  previously  fairly  uncertain.  It 
has,  indeed,  been  estimated  with  probable  correctness  that  in  the  absence 
of  strays  (or  their  practical  elimination)  communication  from  Germany 
to  the  United  States  could  be  carried  on  with  about  ten  kilowatts  in 
the  antenna,  or  even  less.  When  it  is  considered  that  at  present  a  power 
of  two  hundred  kilowatts  in  the  antenna  at  Nauen  is  not  really  always 
sufficient,  the  importance  of  stray  elimination  is  made  increasingly 
evident. 

Radio  telephony  has  one  great  advantage  over  radio  telegraphy  in 
the  matter  of  stray  elimination.  It  is  well  known  that  speech  can  be 
carried  on,  after  a  fashion,  even  under  very  serious  difficulties;  for 
example,  in  extremely  noisy  localities.  The  ease  in  understanding  speech 
under  such  conditions  is  due  particularly  to  our  lifelong  practice,  since 
it  is  rather  unusual  (in  cities  at  least)  to  carry  on  speech  under  condi- 
tions of  even  approximate  silence.  Then,  too,  there  is  what  may  be 
termed  the  "assistance  of  context."  By  this  is  meant  the  ability  of  the 
average  listener  in  "filling  in"  lost  words  in  a  conversation  by  judging 
what  word,  placed  in  the  gap,  would  give  sense  to  the  entire  sentence. 
This  assistance  is  much  greater  than  is  usually  believed,  as  can  be  easily 
shown  by  the  common  experience  in  listening  to  names  over  a  telephone. 
Whereas  ordinary  conversation  is  carried  on  over  normal  telephone  lines 
without  any  particular  difficulty,  the  moment  names  or  figures  (that  is, 
material  lacking  assisting  context)  are  given,  great  difficulty  is  experi- 
enced and  the  percentage  of  errors  rises  markedly. 


20  Assistance  of  Context 

There  is  no  doubt,  therefore,  that  understanding  a  telephone  con- 
versation through  comparatively  heavy  strays  is  a  simpler  achievement 
than  taking  down  telegraphic  signals  under  the  same  conditions. 

We  shall  return  in  some  detail  to  the  methods  used  in  stray  elimina- 
tion, or  reduction,  in  connection  with  receiving  systems  (page  220). 


CHAPTER  II. 

6.  SUSTAINED  WAVE  GENERATORS,      (a)    ARCS;  DUDDELL- 

POULSEN  ARC;  POULSEN  ARC;  FULLER^  METHOD  OP  IN- 
CREASING OUTPUT  EFFICIENCY;  ARCS  OF  DANISH  CONTI- 
NENTAL SYNDICATE;  "FLYWHEEL  CIRCUIT";  ARCS  OF  BER- 
LINER COMPANY;  ARCS  OF  LORENZ  COMPANY;  ARCS  OF 
FEDERAL  TELEGRAPH  COMPANY;  EXPERIMENTS  OF  MAJOR- 
ANA;  ARCS  OF  TELEFUNKEN  COMPANY;  ARCS  OF  COLIN 
AND  JEANCE. 

It  will  be  seen  from  the  previous  treatment  of  the  subject  of  radio 
telephony  that  a  complete  one-way  installation  comprises  a  generator  of 
practically  sustained  waves  at  the  transmitting  station,  a  means  for 
controlling  or  modulating  the  output  thereof,  an  antenna  and  ground 
system  for  radiating  a  portion  of  the  modulated  energy;  and,  at  the 
receiving  station,  an  antenna  and  ground  system,  and  a  radio  receiver 
with  or  without  suitable  amplifying  devices. 

It  is  proposed  to  consider  first  the  various  types  of  sustained  wave 
generators  which  may  be  used  in  radio  telephony. 

6    SUSTAINED  WAVE  GENERATORS, 
(a)  ARCS. 

For  the  sake  of  completeness,  we  shall  give  here  a  description  of 
the  theory  of  the  arc  and  its  historical  development  from  one  of  our 
earlier  papers: 

"The  simplest  generator  of  radio  frequency  oscillations  of  consider- 
able power  is  the  Duddell-Poulsen  arc.  In  Figure  9'is  shown  the  arrange- 
ment used  by  Duddell.  G  is  a  direct  current  generator,  Rr  is  the  resist- 
ance intended  to  control  the  arc  current,  and  If  a  choke  coil  intended 
to  keep  the  alternating  current  out  of  the  generator  and  also  to  steady 
the  supply  voltage.  K  (for  the  Duddell  arc)  has  solid  carbon  electrodes. 
L,  Gy  and  R  are  inductance,  capacity,  and  resistance  inserted  in  the  arc 
shunt  circuit.  Their  values  should  be  carefully  chosen. 

"If  the  arc  be  lit,  it  is  found  that  an  alternating  current  appears 
in  the  shunt  circuit,  and  if  the  frequency  of  this  current  is  within  the 
limits  of  audibility,  a  pure  singing  tone  will  be  heard." 

21 


22 


Equivalent  Resistance  of  Arc 


The  arc  differs  from  ordinary  conductors  in  one  essential  respect. 
If  we  divide  the  potential  difference  (or  voltage)  at  the  terminals  of 
an  ordinary  metallic  conductor  by  the  current  flowing  through  the  con- 


FIGUKE  9 — Typical  arc  circuit. 

ductor,  the  quotient  is  found  to  be  a  constant  quantity  called  the  resist- 
ance of  the  conductor.  This  is  the  case  regardless  of  the  values  of 
voltage  and  current  (at  least,  until  the  conductor  becomes  heated  by 
the  passage  of  excessive  current).  In  the  arc,  the  quotient  of  voltage 
divided  by  current  is  by  no  means  constant.  In  fact,  for  high  voltages 
the  arc  resistance  is  a  large  quantity  and  very  little  current  passes 


FIGURE  10 — Typical  arc  radiophone  transmitter. 


Arcs;  Fuller,  and  Berliner-Poulsen 


23 


•WWW 

»l 


FIGURE  11 — Fuller's  method  of  increasing  arc  efficiency. 


FIGURE  12 — Berliner-Poulsen  arc  for  portable 
stations. 


24 


Arc  of  Danish  Poulsen  Company 


FIGURE  13 — Danish   Poulsen  arc   radiophone   transmitter. 

through  the  arc  under  such  voltages.  For  moderate  voltages,  the  are 
resistance  is  much  less,  and  moderate  currents  pass.  For  low  voltages, 
the  arc  resistance  becomes  exceedingly  small  and  the  arc  current  tends 


WMMp *- 


WVWlAr *• 


FIGURE  14 — Poulsen  radiophone  transmitter  and  receiver. 


Negative  Resistance  of  Arc 


25 


to  increase  indefinitely ;  that  is,  the  arc  is  unstable  and  tends  to  become 
a  short-circuit.  We  are  forced  then  to  the  conclusion,  that  a  small 
increase  in  the  voltage  at  the  terminals  of  an  arc  causes  a  small  decrease 
in  the  resultant  current;  and  consequently  we  sometimes  speak  of  the 
"negative  resistance"  of  an  arc  as  distinguished  from  the  ordinary  or 
positive  and  current-limiting  resistance  of  metallic  conductors. 


• 


FIGURE  15 — Fly-wheel  Poulsen  arc  circuit 
for  radio  telephony. 


' '  The  theory  of  the  action  of  the  singing  arc  is  the  following :  When 
the  condenser  and  the  inductance  in  the  shunt  circuit  are  connected 
to  the  arc,  the  condenser  begins  to  accumulate  a  charge,  and  therefore 
robs  the  arc  of  a  part  of  its  current,  since  the  supply  current  is  kept 
appreciably  constant  by  the  presence  in  the  supply  leads  of  the  choke 
coils  L'.  If  the  current  through  the  arc  decreases,  it  is  clear  from  the 
foregoing  considerations  that  the  voltage  at  its  terminals  must  increase. 
Consequently,  as  long  as  the  charging  of  the  condenser  continues,  the 
arc  voltage  will  rise.  As  soon  as  the  condenser  is  fully  charged,  the 
arc  voltage  becomes  stationary.  Then  the  condenser  begins  to  discharge 


26 


Poulsen  Arc 


itself  through  the  arc,  thereby  increasing  the  arc  current  and  diminish- 
ing the  voltage.  The  shunt  circuit  being  a  true  periodic  or  oscillatory 
circuit,  the  discharge  of  the  condenser  will  continue  past  the  point  of 
zero  current,  and  there  will  occur  an  actual  reversal  of  current.  Thus 
the  condenser  becomes  charged  in  the  negative  direction  until  the  arc 
voltage  falls  so  far  that  the  supply  voltage  of  the  direct  current  gen- 
erator causes  a  reversal  of  the  whole  action.  The  cycle  is  then  repeated, 
and  with  a  frequency  related  to  a  certain  extent  to  that  of  the  natural 
oscillations  of  the  shunt  circuit.  The  mode  of  vibration  which  takes 
place  in  the  arc  is  thus  closely  analogous  to  the  action  in  an  organ  pipe 
of  the  reed  type." 

In  1903,  Poulsen  raised  the  arc  to  the  status  of  a  practically  opera- 
tive generator  of  radio  frequency  energy  in  considerable  quantity  by  the 
following  changes:  placing  the  entire  arc  in  an  atmosphere  of  hydrogen 
or  a  hydrocarbon  vapor  (e.g.,  alcohol  or  gasoline),  using  a  carbon  elec- 
trode for  the  negative  side  and  a  copper  anode  water-cooled  for  the  posi- 
tive side,  rotating  the  carbon  electrode  slowly  by  motor  drive,  and 
placing  an  intense  deflecting  magnetic  field  transverse  to  the  arc. 
Except  for  certain  constructional  and  electrical  details,  this  is  the 
Poulsen  arc  of  to-day. 

In  Figure  10  is  shown  a  typical  arc  radio- 
phone station.  The  arc  K  is  shown  in  the 
magnetic  field  due  to  the  coils  M.  A  is  an  am- 
meter for  measuring  the  antenna  current,  and  T 
is  a  heavy-current  transmitter,  usually  of  the 
carbon  microphone  type.  The  control  methods 
which  may  be  used  with  arcs  other  than  that 
shown  will  be  considered  under  another  head- 
ing. A  modern  improvement  in  arc  transmitters, 
and  one  which  results  in  a  great  increase  in  over- 
all efficiency  of  the  arc,  is  that  shown  in  Figure 
11.  This  is  due  to  Mr.  L.  F.  Fuller,  and  the 
inventor  states  that  very  marked  increases  in 
output  result  when  it  is  used.  It  consists  first: 
in  placing  in  shunt  with  the  arc  and  the  antenna 
series  condenser  Cl  the  condenser  C2  and  second  : 
in  placing  around  the  series  condenser  Ct  an  in- 
ductance LI  and  a  resistance  Rlt  The  chief 
function  of  the  condenser  C2  is  to  act  as  a  by- 
pass for  the  radio  frequency  current,  thereby 
avoiding  passing  through  the  arc  the  entire  an- 
tenna  current  as  well  as  the  direct  supply  cur- 


FIGURE 
Poulre 


16  -  -  Lorenz- 


Poulsen's  Arc  Radio  Telephony 


27 


rent.  The  circuit  L^E^C^  is  tuned  nearly  to  the  frequency  of  the  an- 
tenna current  and  thus  acts  as  an  absorbing  circuit  for  such  currents. 
It  will  therefore  have  the  function  of  a  powerful  choke  circuit  for  the 
arc  and  will  assist  the  condenser  C2  in  its  action. 

Before  discussing  the  actual  results  obtained  by  Poulsen  arc  radio- 
phone transmitters,  we  shall  show  the  types  of  construction  of  such  arcs 
in  sizes  rated  from  250  watts  to  100  kilowatts.  The  first  of  these,  shown 
in  Figure  12,  is  a  small  portable  military  station  made  by  the  Telephone 
Manufacturing  Corporation  of  Vienna.  In  this  case,  the  carbon  is  ro- 
tated at  intervals  by  hand,  and  the  alcohol  feed  into  the  arc  chamber 
is  accomplished  automatically  by  the  vaporization  of  the  alcohol  by  the 
heat  of  the  arc. 

As  early  as  1906,  Poulsen  established  radiophonic  communication 
over  a  distance  of  about  600  feet  (200  m.)  using  antennas  only  15  feet 
(5  m.)  high.  In  1907,  with  the  equipment  shown  in  Figure  13,  com- 
munication was  established  between  Esbjerg  and  Lyngby,  a  distance  of 
170  miles  (270  km.).  The  antenna  height  was  200  feet  (60  m.),  the 
wave-length  1,200  meters,  the  arc  supply  power  900  watts,  and  the  an- 
tenna power  300  watts.  Later,  phonograph  music  was  heard  in  Berlin 
after  transmission  from  Lyngby  a  distance  of  about  300  miles  (500  km.). 
In  Figure  13.  the  arc  is  shown  to  the  extreme  right,  and  the  multiple 
microphone  transmitter  (six  microphones  in  series)  in  the  middle  of  the 
figure.  The  arc  was  in  its  own  primary  circuit  in  this  case,  and  coupled 
inductively  to  the  antenna.  At  the  left,  the  inductively  coupled  receiv- 
ing set  is  shown.  The  secondary  circuit  was  made  aperiodic  by  placing 


frvr?  Carton 
Hotter 


FIGURE  17 — Construction  of  Lorenz-Poul- 
sen  arc  for  radio  telephony. 


28  "Fly- Wheel"  Circuit;  Lorenz  Arcs 

the  detector  directly  in  series  with  the  secondary  coupling  inductance  and 
without  any  secondary  tuning  condenser.  The  reasons  for  this  type  of 
receiver  will  be  discussed  under  another  heading.  In  Figure  14  are 
illustrated  the  arrangements  used.  It  will  be  noted  that  the  microphones 
are  shunted  by  the  condenser  (7,  thereby  making  the  transmission  partly 
one  by  change  of  wave-length  as  well  as  by  change  in  antenna  energy. 

When  small  antennas  of  high  intrinsic  decrement  are  used,  an  ar- 
rangement known  as  a  "fly- wheel  circuit"  may  be  employed.  This  is 
shown  in  Figure  15.  The  circuit  LC  is  inserted  in  the  antenna,  L  being 
large  in  comparison  with  the  antenna  inductance,  The  wave-length  of 
the  radiated  energy  will  consequently  be  approximately  that  of  the  cir- 
cuit LC.  In  this  way,  energy  may  be  stored  in  the  highly  undamped 
circuit  LC  and  gradually  radiated.  The  two  condensers  C"  are  not 
essential  to  the  operation  and  serve  only  to  keep  the  direct  current  sup- 
ply leads  from  conductive  connection  to  antenna  and  ground  thereby 
avoiding  the  possibility  of  serious  high  voltage  shocks  when  touching 
the  antenna.  In  the  case  shown,  the  microphone-shunting  condenser,  C' 
has  a  value  between  0.05  and  0.20  microfarad. 

In  Figure  16  is  given  a  photograph  of  an  arc  rated  at  about  100 
watts  output,  and  built  by  the  C.  Lorenz  Company  of  Berlin  specially  for 
radio  telephony.  Its  construction  is  shown  in  Figure  17.  The  carbon 
holder  is  of  iron,  and  forms  the  open  core  of  a  circular  multi-layer  coil 
which  produces  a  moderately  strong  magnetic  field  passing  directly  up- 
ward through  the  carbon.  The  field  then  spreads  outward  to  the  upper 
iron  ring,  passing  radially  through  the  arc  in  so  doing.  In  consequence 
of  the  presence  of  this  field,  the  arc  will  slowly  rotate  around  the  edge 
of  the  carbon,  thereby  causing  even  wear.  The  copper  electrode  is  held 
within  the  iron  ring,  and  provided  with  massive  cooling  flanges.  In 
Figure  16,  the  alcohol  sight-feed  cup  is  seen  at  the  top,  and  the  vertical 
cooling  flanges  below  and  to  the  right.  The  insulator  between  the  upper 
and  lower  electrodes  is  a  heavy  ring  with  flat  faces,  made  of  plaster 
with  asbestos  facings.  The  clamping  screws  are  also  visible,  as  are  the 
two  poppet  safety  valves  which  relieve  the  excessive  pressure  resulting 
when  the  arc  is  first  lit  and  the  mixture  of  alcohol  vapor  and  air  explodes. 
The  lower  electrode  holder  and  the  surrounding  coil  are  just  below  the 
middle  of  the  illustration. 

One  of  the  defects  of  these  small  arcs  is  the  necessity  for  adjusting 
the  arc  length  occasionally  as  the  carbon  burns  away.  To  overcome  this, 
the  Lorenz  Company  has  built  a  self-regulating  arc  provided  with  a 
mechanism  somewhat  like  the  magnetic  length-control  of  an  ordinary 
street  lighting  arc.  The  device  is  supposed  to  be  very  effective  in 
practice. 


Arcs  of  Berliner-Poulsen  Company 


29 


FIGURE  18 — 3  k.  w.  Berliner-Poulsen  arc. 

A  somewhat  larger  type  of  arc  of  3  k.w.  input  made  by  the  Tele- 
phone. Manufacturing  Corporation  (formerly  J.  Berliner),  of  Vienna,  is 
illustrated  in  Figure  18.  It  will  be  noted  that  provisions  are  made  here 
for  an  extremely  intense  magnetic  transverse  field.  While  this  is  of 
advantage  in  increasing  the  available  radio  frequency  output,  it  tends 
to  cause  a  certain  degree  of  irregularity  in  the  output  with  a  resultant 
crackling  noise  or  hissing  in  the  received  speech.  This  last  defect 
may  prove  extremely  serious,  so  that  magnetic  fields  on  arcs  used  for 
radio  telephony  must  be  employed  with  caution,  and  with  associated 
circuits  and  outputs  which  minimize  arc  unsteadiness.  In  Figure  18,  the 
small  motor  which  rotates  the  carbon  electrode  is  seen  in  the  lower  cen- 
tral portion,  and  there  are  also  shown  the  sections  of  the  magnetic  field 
whereby  the  field  strength  may  be  conveniently  varied.  The  heavy  in- 
sulation surrounding  the  push  button  used  for  striking  the  arc  at  the 


30 


Poulsen  Arcs 


beginning  of  operation  is  a  necessary  adjunct  since  disagreeable  burns 
are  easily  sustained  when  using  high  power  arcs  carelessly.  An  arc  of 
somewhat  smaller  output  than  that  shown  is  guaranteed  by  the  makers 
for  telegraphy  over  125  miles  (200  km.)  when  using  portable  masts,  but 
for  only  about  12  or  15  miles  (25  km.)  for  radio  telephony. 

A  somewhat  larger  type  of  arc,  built  by  the  Danish  Poulsen  Com- 
pany (Det  Kontinental  Syndikat),  is  shown  in  front  view  in  Figure  19. 
The  massive  field  magnet  coils,  the  driving  motor  for  the  carbon  holder, 
and  the  arc  striking  and  adjusting  knobs  are  visible.  It  is  to  be  noted 
that  all  arcs  giving  any  considerable  output  have  air  core  choke  coils 
in  the  feed  circuit,  since  the  distributed  capacity  of  iron  core  coils  gives 
rise  to  the  possibility  of  injurious  resonance  phenomena  inside  the  coils 
and  may  permit  radio  frequency  currents  to  pass. 


FIGURE  19 — Continental  Syndicate  Poulsen  arc. 

An  arc  made  by  the  Berliner  Company  of  Vienna,  and  having  an 
input  of  10  to  25  kilowatts  is  illustrated  in  Figure  20.  As  will  be  seen, 
it  is  provided  with  an  automatic  ignition  device,  a  device  for  the  indica- 
tion of  arc  length  or  wear  of  the  carbon  electrode,  a  mixing  chamber 
of  glass  for  the  gas  used  in  the  arc,  and  a  complete  water  cooling  system 
for  the  field  magnet  coils  as  well  as  for  the  arc. 

Some  interesting  information  relative  to  Poulsen  arc  radiophones  of 
the  type  shown  in  Figure  21  is  given  by  Captain  Anderle.  Figure  21 
is  a  ship  station  of  a  complete  type,  being  used  for  either  telegraphy  or 
telephony.  The  arc,  which  is  normally  rated  at  about  8  kilowatts  input, 
is  shown  at  the  left.  For  telephony,  it  is  used  at  reduced  power,  inas- 
much as  the  multiple  microphone  transmitter  at  the  right  would  be 


Berliner-Poulsen  Arcs 


31 


FIGURE  20 — Berliner  25  k.  w.  Poulsen  arc. 

incapable  of  modulating  the  full  output.  About  3.5  amperes  (and  never 
over  4)  are  passed  through  the  transmitters,  which  are  placed  directly 
in  the  ground  lead  of  the  antenna.  With  masts  150  feet  (45  m.)  high, 
distances  of  from  30  to  60  miles  (50  to  100  km.),  are  covered  over  flat 


32 


Berliner-Poulsen  Arc  Radiophones 


country.  The  speaker  is  warned  to  speak  distinctly  but  not  too  loudly, 
with  the  mouth  held  near  the  transmitter.  It  is  recommended  to  tap  the 
microphones  occasionally,  or  to  have  alternative  sets  so  that  overheating 
of  one  set  does  not  occur. 


FIGURE  21 — Berliner-Poulsen  arc  ship  radiophone  station. 


FIGURE  22 — Berliner-Poulsen  3  k.  w.  arc  radiophone  station. 


Poulsen  Arc  of  Berliner  Company 


33 


In  Figure  22  is  shown  an  unusually  complete  set  of  the  Poulsen 
arc  type  built  by  the  Berliner  Company  of  Vienna.  This  set  is  adapted 
at  the  same  time  to  ordinary  arc  telegraphy,  multi-tone  arc  telegraphy, 
and  radio  telephony.  The  arc  is  of  3  k.w.  input,  being  the  same  as 
that  given  in  Figure  18.  The  telegraphic  range  of  this  set  is  given  as 
375  miles  (600  km.).  The  receiving  set  and  test  buzzer  are  mounted 
on  the  right  hand  portion  of  the  long  table;  the  arc  and  key  at  the 
left  center ;  the  relay  key  and  transfer  switches  are  to  the  left  of  the  arc 
near  the  variable  transmitting  coupling  and  the  multi-tone  control  key- 
board. In  the  extreme  left  foreground  is  the  large  microphone  trans- 
mitter, to  be  described  hereafter  when  control  systems  are  considered. 


FIGURE  23 — Federal  Telegraph  Company  00  k.  w. 
Poulsen  arc  at  Tucker  ton. 


34 


Arc  of  Federal  Telegraph  Company 


Although  the  newer,  high  power  arcs  are  not  yet  employed  for  radio 
telephony  because  of  the  great  difficulty  in  modulating  the  output,  never- 
theless they  form  a  possible  direction  of  radio  telephonic  development* 
Accordingly,  we  show  in  Figure  23  an  arc  of  60  k.w.  input  made  by 
the  Federal  Telegraph  Company,  this  corresponding  to  500  volts  and 
120  amperes.  It  is  this  arc  which  has  carried  a  portion  of  the  trans- 
Atlantic  traffic  from  Tuckerton,  New  Jersey,  to  Hanover,  Germany,  a 
distance  of  4,000  miles  (6,500  km.).  In  this  case,  the  antenna  current 
was  120  amperes,  the  arc  standing  considerable  overload.  We  also  show, 
in  Figure  24,  a  100  k.w.  arc  made  by  the  same  Company,  and  used 
for  communication  between  the  United  States  Naval  Radio  Station  at 
Darien,  Panama  Canal  Zone  and  "Washington,  a  distance  of  1,900  miles 
(3,000  km.).  It  will  be  seen  that  both  these  arcs  are  very  sturdily 
designed  and  provided  with  an  unusually  rugged  and  elaborate  water- 
cooling  system. 


FIGURE  24 — Federal  Telegraph  Company  100  k.  w.  Poulseii  arc  at  Darien. 

The  Federal  Telegraph  Company  carried  on  radiophone  experiments 
from  1910  through  1912  between  the  stations  at  San  Francisco,  Stockton, 
Sacramento,  and  Los  Angeles  (all  in  California).  The  distance  between 
any  two  of  the  first  three  stations  mentioned  is  90  miles  (140  km.)  and 
between  the  first  and  the  last  station  mentioned  355  miles  (570  km.). 
Speech  between  San  Francisco,  Stockton,  and  Sacramento  was  clear  at 
all  times,  but  between  these  points  and  Los  Angeles  it  was  weak  and 
indistinct.  The  antenna  heights  were  300  feet  (94  m.) 


Arc  Radiophone  Experiments  of  Majorana  35 

Before  leaving  the  subject  of  the  Poulsen  are,  it  is  of  interest  to  give 
detailed  accounts  of  just  what  has  been  accomplished  by  these  methods 
in  addition  to  the  achievements  already  mentioned. 

A  remarkable  series  of  experiments  were  made  by  Q.  Majorana  in 
1908.  The  results  obtained  are  best  described  in  the  words  of  Majorana 
himself : 

"The  first  research  was  conducted  in  the  Istituto  Superiore  del 
Telegrafia  in  Rome.  The  antenna  was  78  feet  (24  m.)  high  and  had 
four  wires.  For  two  years,  I  have  been  conducting  experiments  between 
this  station  and  a  government  naval  station  at  Monte  Mario,  3  miles 
(5  km.)  away.  The  antenna  at  the  latter  station  had  also  four  wires 
and  was  about  175  feet  (50  m.)  high.  An  ammeter  in  the  antenna  at 
the  former  station  showed  under  normal  conditions  of  working  a  reading 
of  about  1.2  amperes.  At  Monte  Mario,  using  the  thermo-electric 
(crystal)  detector,  a  current  of  15  micro-amperes  was  obtained.  Words 
spoken  in  Rome  could  be  heard  at  Monte  Mario  by  the  use  of  a  Marconi 
magnetic  detector,  but  could  be  heard  very  much  more  loudly  and  clearly 
by  the  use  of  the  former  detector. 

"Because  of  these  results,  the  Naval  Bureau  provided  a  second 
research  station  at  Porto  d' Anzio,  25  miles  (56  km.)  from  Monte  Mario, 
with  a  four-wire  antenna  145  feet  (45  m.)  high.  On  the  13th  of  August, 
1908,  the  experiment  was  tried,  and  this  showed  that  with  a  current 
strength  of  3.5  amperes  in  the  antenna  at  Monte  Mario  any  words  spoken 
in  Rome  could  be  very  distinctly  heard  at  Anzio. 

"Hereupon  the  Naval  Bureau  ordered  that  these  researches  should 
be  carried  on  over  longer  ranges.  The  torpedo  boat  'Lanciere'  was 
accordingly  put  at  my  disposal,  and  arrived  on  the  13th  of  November  at 
the  Island  of  Ponza,  about  75  miles  (120  km.)  from  Monte  Mario.  On 
this  island  there  is  a  station  for  radio  telegraphy,  with  an  antenna  of 
four  wires  about  200  feet  (60  m.)  high.  Using  the  same  receiving 
apparatus  as  had  been  employed  at  Rome,  words  spoken  in  Rome  could 
be  heard  at  Ponza  with  greater  loudness  even  than  at  Anzio ;  the  vibra- 
tions of  the  telephone  diaphragm  could  be  heard  at  a  distance  of  10  or 
15  feet  (3  or  4  m.).  The  superiority  of  these  results  is  to  be  ascribed 
to  the  better  location  of  the  station  at  Ponza. 

"On  the  14th  of  November,  the  'Lanciere'  landed  at  Maddalena  in 
Sardinia.  The  nearby  station  at  Becco  di  Vela,  which  is  similar  to  that 
at  Ponza,  was  then  used.  The  station  is  about  170  miles  (270  km.) 
from  Rome  in  an  air  line.  On  that  day,  at  12  o'clock,  attempts  to 
communicate  with  Rome  were  repeated  and  again  gave  excellent  results. 


36  Arc  Radiophone  Experiments  of  Poulsen 

The  voice  at  Monte  Mario  was  distinctly  audible,  and  the  strength  of  the 
speech  was  not  less  than  it  is  in  the  ordinary  wire  telephone  in  use  in  the 
city.  We  can,  therefore,  state  that  over  this  range  a  practically  workable 
radio  telephonic  service  can  be  provided. 

"Finally,  I  desired  to  find  the  utmost  range  of  the  radio-telephonic 
apparatus  at  my  disposal.  On  the  1st  of  December,  the  'Lanciere' 
arrived  at  Trapani,  in  Sicily,  where  further  attempts  were  made,  using 
the  radio-telegraphic  station  at  Monte  San  Giuliano.  This  station 
resembles  that  at  Ponza,  and  is  270  miles  (420  km.)  in  an  air  line  from 
Rome.  It  took  quite  some  effort  to  secure  sharp  tuning  here,  partly 
because  of  considerable  interference  from  a  neighboring  station,  but 
finally  the  spoken  word  from  Rome  could  be  heard,  even  though  it 
was  faint  and  not  easy  to  understand.  The  intensity  in  this  case  was 
barely  sufficient  for  the  trained  ear  to  read.  We  were  here  at  the  limit 
of  the  range.  This  was  proved  more  clearly  on  the  following  day.  At 
Forte  Spurio  is  a  station  which  is  about  as  far  from  Rome  as  that  on 
San  Giuliano,  but  less  favorably  situated.  I  went  to  Forte  Spurio  and 
found  that  the  words  sent  from  Rome  could  not  be  heard  there. 

"The  utmost  range  of  my  system  was  by  no  means  reached  in  these 
experiment,  for  the  hydraulic  microphone  was  not  used  to  a  point  even 
approaching  its  full  capacity. "  (Majorana  used  a  Poulsen  arc  generator, 
but  modulated  the  antenna  energy  by  means  of  a  special  hydraulic 
transmitter  which  will  be  described  under  control  systems,  page  152.) 

"I  desire  to  mention  one  important  point  in  these  experiments. 
After  several  trials,  it  was  positively  shown  that  the  quality  of  the  word 
was  not  altered,  even  at  distance  of  250  miles  (400  km.).  That  is,  the 
articulation  was  clear  and  the  fine  inflections  of  the  voice  were  preserved. 
This  is  because  all  the  various  frequencies  contained  in  the  speech  suffer 
the  same  weakening  for  equal  distances,  so  that  there  is  no  distortion  of 
the  speech.  With  the  ordinary  telephone  lines,  on  the  other  hand,  the 
propagation  depends  largely  on  the  acoustic  period ;  in  radio  telephony, 
the  period  of  the  electro-magnetic  radio  frequency  oscillations  is  of  the 
greatest  importance." 

Experiments  were  carried  on  at  the  end  of  June,  1909  between  the 
large  Poulsen  stations  in  Denmark  at  Lyngby  and  Esbjerg,  the  distance 
between  these  stations  being  170  miles  (280  km.).  The  Egner-Holm- 
strom  heavy  current  microphone,  to  be  described  later  (page  144),  was 
used  directly  in  the  transmitting  antenna.  Such  microphones  can 
carry  10  to  15  amperes,  but  it  was  shown  that  this  current  was  un- 
necessary for  the  range  in  question.  In  fact,  with  an  antenna  current 
of  6  amperes  properly  modulated,  communication  of  a  very  good  and 


Arcs  of  Telefunken  Company 


37 


clear  sort  ("sehr  gut  and  deutlich"  according  to  the  experimenters) 
was  established. 

An  arc  system  of  radio  telephony  distinguished  by  simplicity  rather 
than  by  efficiency  or  perfect  reliability  in  practice  has  been  developed 
by  the  Telefunken  Company,  though  it  has  been  superseded  by  their 
radio  frequency  alternator-frequency  changer  methods  to  be  described 
later. 

The  arcs  used  by  the  Telefunken  Company  were  burned  either  six 
in  series  on  220  volts  direct  current,  twelve  in  series  on  440  volts,  or 
twenty-four  in  series  on  880  volts.  They  burned  practically  in  the  open 
air.  The  lower  carbon  electrode  rested  in  a  depression  in  the  base  of  a 
large,  hollow,  copper  cylinder  filled  with  water,  which  cylinder  formed 
the  other  electrode.  The  water  naturally  served  for  cooling,  and  the 
carbon  dioxide  formed  by  the  slow  combustion  of  the  carbon  remained 
partially  in  the  depression  mentioned,  and  prevented  the  further  and 
free  access  of  air  to  the  arc.  No  magnetic  field  was  used  with  the 
arcs  in  question,  and  the  efficiency  was  low.  With  an  energy  consump^ 
tion  of  6  kilowatts  for  24  arcs  in  series,  only  about  10  per  cent,  of  the 
available  energy  was  converted  into  the  radio  frequency  form.  However, 
the  carbon  electrodes  which  were  3.5  cm.  (1.4  inches)  in  diameter  burned 
nearly  200  hours  for  each  half  inch  of  length. 


FIGURE  25 — Telefunken  Company  series  arc 
radiophone    transmitter. 


38 


Arc  Radiophone  of  Telefunken  Company 


FIGURE  26 — Telefunken  series  arc  radio  transmitter. 

The  arcs  were  arranged  as  illustrated  in  Figure  25.  It  will  be  seen 
that  all  six  could  be  struck  at  once  by  the  right-hand  handle,  and  that 
the  length  of  each  arc  could  be  adjusted  individually  by  a  separate 
adjustment  screw  (not  shown  in  the  illustration).  The  actual  wiring  of 
the  set  is  shown  in  Figure  26,  and  presents  some  valuable  features.  To 
begin  with,  there  is  a  switch,  X,  which  not  only  transfers  the  antenna 
connection  from  the  transmitter  to  the  receiver,  but  short-circuits  the 
receiver  while  transmission  is  going  on,  by  the  use  of  auxiliary  contacts, 
not  shown.  The  switch,  Y,  connects  together  the  points,  Q  and  8,  while 


FIGURE  27 — Colin  and  Jeance  radiophone  transmitter. 


Arcs  of  Colin  and  Jeance  39 

sending  is  going  on  and  the  arc  is  oscillating.  While  receiving  is  going 
on,  the  oscillations  are  stopped  by  opening  the  connection  between  Q  and 
S.  At  the  same  time,  the  resistance,  R,  becomes  operative  in  holding 
down  the  direct  arc  current.  During  transmission  the  alternating  cur- 
rent generated  by  the  arc  passes  through  the  condenser,  C,  while  only  the 
direct  current  passes  through  R.  In  this  ingenious  way,  the  arc  current 
is  prevented  from  rising  markedly  when  the  oscillations  cease,  which  is 
otherwise  the  case.  The  microphone  is  seen  to  be  connected  across  the  an- 
tenna tuning  inductance,  which  also  serves  for  coupling.  Consequently, 
the  microphone  has  the  triple  purpose  of  diminishing  the  coupling, 
shortening  the  radiated  wave-length,  and  diminishing  the  antenna  cur- 
rent by  dissipating  a  portion  of  the  available  energy. 

On  November  15,  1907,  using  the  apparatus  just  described,  radio- 
phone speech  was  transmitted  from  Berlin  to  Rheinsberg,  a  distance  of 
about  45  miles  (75  km.),  the  mast  heights  being  85  feet  (26  m.),  and 
the  input  power  440  volts  and  5  amperes. 

In  1908,  a  system  of  radio  telephony  developed  by  Lieutenants 
V.  Colin  and  M.  Jeance  of  the  French  Navy  was  first  thoroughly  tried 
out.*  There  were  used  three  arcs  in  series  supplied  with  600  volts,  the 
three  being  regulated  simultaneously  (and  in  later  models  automatically) . 
An  oscillatory  circuit  is  shunted  around  the  arc,  and  coupled  to  an 
intermediate  circuit,  to  which  the  antenna  is  coupled  in  turn.  The 
positive  electrodes  are  heavy  copper  cylinders  with  cooling  (usually  by 
an  interior  stream  of  kerosene),  and  the  negative  electrodes  are  carbon 
rods  of  extremely  small  diameter  (1  or  2  mm.,  i.  e.,  0.04  to  0.08  inch), 
the  arcs  taking  place  in  an  atmosphere  of  some  hydrocarbon  such  as 
illuminating  gas,  acetylene,  gasoline,  alcohol,  heavy  oils,  etc. 

Under  these  conditions,  the  positive  electrodes  are  not  attacked  at 
all,  and  the  negative  (carbon)  electrodes  merely  increase  slowly  and 
regularly  in  length  because  of  the  deposition  thereon  of  a  fine  layer 
of  carbon  from  the  hydrocarbon  atmosphere.  Consequently,  the  arc  does 
not  tend  to  wander  about  the  electrodes  as  is  usual. 

In  order  to  ensure  purity  of  the  radiated  wave  and  freedom  from 
overtones  (which  are  apt  to  prove  troublesome,  particularly  for  arcs  in 
powerful  magnetic  fields,  or  arcs  from  which  excessive  energy  is  being 
drawn),  the  arc  oscillating  circuit  is  coupled  to  the  antenna  by  means  of 
an  intermediate  tuned  circuit  which,  in  turn,  is  inductively  coupled 
to  the  antenna. 

The  microphone  transmitters  are  of  special  design  and  contain 
no  combustible  material,  the  grain  carbon  being  placed  in  cavities  cut 


*  For  much  of  the  information  here  given,  the  Author  is  indebted  to  the  "Bulletin  de 
la  Societ6  Internationale  des  Electriciens,"   for  July,   1909. 


40 


Arc  Radiophone  of  Colin  and  Jeance 


into  sheets  of  marble   or  slate.     The  vibrating  diaphragm  is  held  at 
a  suitable  distance   from  the  carbon  support  by  a  metal  washer. 

The  actual  circuit  employed  during  some  tests  in  1914  is  shown  in 
Figure  27.  Here  G  is  a  650  volt  direct  current  generator,  which  fur- 
nished in  the  tests  in  question  4.2 
amperes  (that  is,  2.73  k.w.).  This 
current  passed  through  the  choke 
coils  L  and  Z/,  and  the  large  regulat- 
ing resistance,  R,  to  the  arcs  which 
are  shown  schematically  in  cross  sec- 
tion. The  relative  size  of  the  elec- 
trodes and  the  method  of  admitting 
the  hydrocarbon  gas  atmosphere  are 
indicated.  The  potential  difference 
across  the  arcs  in  this  case  was  350 
volts,  and  consequently  the  energy 
consumption  in  the  arc  was  1.47  k.w., 
leaving  1.26  k.w.  to  be  absorbed  in  the 
circuit  of  the  generator,  G  and  prob- 
ably mainly  in  the  resistance  R.  The 
intermediate  circuit,  L2C2L2',  was 
very  slightly  damped,  the  capacity, 
C2,  being  large.  It  will  be  noted  that 
the  microphone,  M,  is  shunted  across 
a  portion  of  the  antenna  coupling  and 
tuning  inductance,  being  itself  in 
series  writh  an  inductance.  It  will 
thus  have  the  triple  function  of  alter- 
ing the  coupling  to  the  intermediate 
circuit,  altering  the  radiated  wave- 
length, and  absorbing  intermittently  a 
portion  of  the  available  radio  fre- 
quency energy.  The  main  antenna 
current  was  3.2  amperes  at  a  wave- 
length of  985  meters,  and  the  current  through  the  microphones  was  0.5 
ampere.  Nine  microphones  in  series  were  employed,  and  two  sets  were 
provided  for  alternate  use  to  avoid  overheating. 

The  arc  carbons  in  these  tests  were  1.5  mm.  (0.06  inch)  in  diameter, 
and  the  arc  took  place  in  an  atmosphere  of  acetylene  (from  calcium  car- 
bide and  water)  mixed  readily  in  proper  proportions  with  hydrogen 
(from  calcium  hydride  and  water).  Under  these  conditions,  the  arcs 
were  not  burnt  away;  in  fact,  the  carbons  increased  slightly  in  length 


FIGURE  28 — Motor  generator  control 

panel  of  Compagnie  Generate  de 

Radiotelegraphie-Colin-Jeance 

Radiophone  Transmitter. 


Arc  Radiophone  of  Colin  and  Jeance 


41 


with  operation.     Independent  arc  length  regulation  was  provided  for 
each  arc,  but  was  not  found  necessary. 

Flat  spirals  of  copper  strip  were  employed  in  the  various  circuits, 
and  either  air  variable  condensers  or  glass  fixed  condensers.  An  aux- 
iliary tone  circuit  shunted  around  the  arc  was  provided  (not  shown  in 
the  figure),  whereby  musical  note  telegraphy  could  be  easily  accom- 
plished. Since  the  total  terminal  arc  voltage  dropped  from  350  to  about 
150  when  not  transmitting,  an  auxiliary  resistance  was  provided  in  the 


FIGURE  .29 — Colin   and    Jeance   series   en- 
closed arcs,  automatic  regulator, 
and  control  apparatus. 


42 


Arc  Radiophone  of  Colin  and  Jeance 


supply  circuit  which  was  automatically  shunted  into  circuit  whenever 
reception  was  begun. 

With  the  equipment  shown,  communication  was  maintained  between 
Paris  and  Mettray,  a  distance  of  200  kilometers  (125  miles). 

In  Figures  28,  29,  30,  and  31  are  shown  the  various  assembled  por- 
tions of  a  modern  complete  set  of  this  type,  as  manufactured  by  the 
Compagnie  Generale  de  Radiotelegraphie.  The  panel  of  Figure  28 
supports  the  motor  and  generator  switches,  measuring  instruments,  and 
control  rheostats.  The  three  arcs  and 
their  enclosing  chamber  together  with 
the  arrangement  for  their  gas  sup- 
ply are  illustrated  in  the  upper  part 
of  Figure  29.  An  automatic  regu- 
lator for  the  arcs  is  mounted  directly 
in  front  of  them.  In  the  lower  por- 
tion of  the  table  are  mounted  the  sup- 
ply circuit  choke  coils  and  resistances. 
The  means  for  tuning  the  primary, 
intermediate,  and  secondary  (or  an- 
tenna) circuits  are  provided  in  the 
cabinet  shown  in  Figure  30.  The  hot 
wire  ammeter  at  the  top  is  in  the 
intermediate  circuit.  The  two  coup- 
lings between  the  pairs  of  circuits 
are  controlled  by  the  projecting 
handles.  Figure  31  illustrates  the 
operator's  table.  The  measuring 
instruments  are  the  antenna  am- 
meter, the  microphone,  shunt  circuit 
ammeter,  and  a  voltmeter  across  the 
arcs.  The  resistance  to  the  right  is 
in  the  microphone  circuit.  .The  two 
microphone  mouthpieces  and  reversed 
horns  and  the  change-over  switch 
between  sets  of  microphones  are  also 
on  the  back  panel.  On  the  table  top 
are  the  antenna  switch,  a  change-over 
switch  from  telegraphy  to  telephony, 


FIGURE    30 — Colin    and    Jeance 

primary,  intermediate,  and 

secondary  control  panel. 


the  sending  key,  the  enclosed  detectors,  and  a  complete  receiving  ap- 
paratus. This  last  is  of  normal  type,  having  inductive  coupling  between 
the  antenna  and  secondary  circuits,  a  tuned  secondary,  and  crystal 
detector. 


Arc  Radiophone  of  Colin  and  Jeance 


43 


FIGURE    31 — Colin    and    Jeance    transmitting    and 
receiving  operator's  table  for  radio  telephony. 


CHAPTER  III. 

(b)  RADIO-FREQUENT  SPARKS  ;  INVERSE  CHARGE  FREQUENCY  ; 
EXPERIMENTS  OF  RUHMER;  EXPERIMENTS  OF  DUBILIER; 
LORENZ  COMPANY  "MULTITONE"  SYSTEM;  SYSTEM  OF  VON 
LEPEL  ;  EXPERIMENTS  OF  CHAFFEE,  AND  CUTTING  AND  WASH- 
INGTON; DITCHAM  SYSTEM;  T.  Y.  K.  SYSTEM;  HANSCOM 
TRANSMITTER;  DE  FOREST  B.C.  AND  A.C.  SYSTEMS;  EXPERI- 
MENTS OF  MORETTI ;  EXPERIMENTS  OF  VANNI ;  EXPERIMENTS 

OF  GOLDSCHMIDT  AND  SCHEIDT-BOON ;  EXPERIMENTS  OF 
MARZI  BROTHERS;  MARCONI'S  " TIMED  SPARK"  METHOD. 

(b)  RADIO-FREQUENT  SPARKS. 

It  has  occurred  to  a  number  of  investigators  that  practically  sus- 
tained radiation  could  be  secured  in  an  antenna  by  using  spark  trans- 
mitters, but  having  these  transmitters  so  arranged  that  the  extremely 
high  frequency  of  the  sparks  (above  the  limits  of  audibility)  would 
render  the  usual  "spark  tone"  inaudible.  If,  then,  the  antenna  energy 
were  modulated  by  a  microphone  or  otherwise,  radio  telephony  would 
become  possible.  To  specify  in  further  detail,  imagine  a  special  form  of 
spark  gap  and  associated  circuit  so  arranged  that  discharges  occurred 
more  or  less  regularly  across  the  gap  at  an  average  frequency  of,  say, 
50,000  sparks  per  second.  If  the  circuit  in  which  these  sparks  occurred 
were  connected  inductively  to  an  antenna,  there  would  be  produced  in 
the  antenna  practically  sustained  radiation,  susceptible  to  suitable  tele- 
phone modulation  by  a  microphone  transmitter  or  otherwise. 

In  Figure  32  is  given  a  graphic  delineation  of  the  effects.  It  will  be 
noticed  that  highly  damped  oscillations  occur  rather  irregularly  in  the 
primary  circuit,  and  that  each  of  these  short  oscillation  groups  starts 
a  decadent  wave  train  which  has  still  a  large  current  amplitude  when 
the  succeeding  spark  takes  place.  Inasmuch  as  the  sparks  follow  each 
other  so  frequently  and  since  the  antenna  circuit  damping  is  low,  the 
effect  at  the  distant  receiver  would  be  appreciably  that  of  sustained  radia- 
tion at  the  transmitter,  and  particularly  is  this  the  case  since  the  changes 
in  antenna  radiation  occur  above  audio  frequency.  Most  of  the  radio- 
frequent  spark  transmitters  for  radio  telephony  operate  in  the  fashion 
indicated,  but  there  is  a  second  special  case,  which  has  certain  interesting 

44 


Radio-Frequent  Sparks 


45 


features.  It  is  illustrated  in  Figure  33,  and  occurs  with  the  Chaffee 
"arc"  (which  is  really  a  spark  phenomenon).  To  begin  with,  in  this 
case  the  spark  gap  has  such  excessively  high  intrinsic  damping  that  the 
spark  discharges  in  the  primary  circuit  tend  to  be  aperiodic.  (The 
structure  of  the  Chaffee  arc  is  described  on  page  56.) 


Primary 


Hr 


77me 


Secondary 


FIGURE  32 — Irregular  radio-frequent  spark 
excitation  of  antenna. 


Primary 


1 


Secondary 


T/me 


FIGURE  33 — Regular  radio-frequent  impulse 
excitation  of  antenna. 


46  Inverse  Charge  Frequency 

The  tendency  toward  aperiodicity  just  mentioned  is  enhanced  by 
Chaffee  in  that  he  couples  the  secondary  circuit  very  closely  to  the 
primary,  thereby  obtaining  a  "quenching"  action  through  the  secondary 
reaction  on  the  primary.  In  addition,  the  direct  current  feed  circuit  of 
the  arc  and  the  coupling  to  the  energy-absorbing  secondary  are  so  ar- 
ranged that  the  spark  frequency  is  an  integral  fraction  (e.  g.,  one-half, 
one-third,  one-fourth,  etc. )  of  the  fre- 
quency of  the  oscillations  in  the  sec- 
ondary circuit.  Thereby  it  occurs 
that  the  successive  discharges  come  at 
just  the  right  time  to  be  in  phase  with 
the  secondary  (or  antenna)  oscilla- 
tions, and  not  at  random  (with  pos- 
sible interference)  as  is  the  case  for 
the  conditions  illustrated  in  Figure  32. 
In  Figure  34  are  shown  oscillograms 
of  the  actual  phenomena.*  Chaffee 


uses  the   term   "inverse   charge   fre- 
quency"  for  the   ratio   between   the 


FIGURE  34 — Primary  and  secondary 

current  with  Chaffee  gap. 
(Inverse  charge  frequency  =  3) 

radio  frequency  in  the  secondary  circuit  and  the  spark  frequency  in  the 
primary  circuit.  The  inverse  spark  frequency  is  a  whole  number  for 
the  Chaffee  arc. 

In  general,  spark  methods  of  radio  telephony  are  open  to  very 
serious  objections.  Unless  the  sparks  not  only  follow  with  great  regu- 
larity but  also  have  nearly  equal  current  amplitudes  (neither  of  which 

conditions  are  easily  fulfilled,  par- 
ticularly in  steady  operation),  there 
will  be  produced  in  the  receivers  of 
the  distant  station  an  annoying  hiss- 
ing sound,  which  will  interfere  seri- 
ously with  clear  articulation  in  the 
speech.      This    accounts,    naturally, 
FIGURE  35— Ruhmer  moving   wire  arc    for  the   frequently  poor   quality   of 
for  radio  telephony.  spark  radiophone  transmitters. 

Nevertheless,  many  investigations  have  been  carried  on  in  these 
directions,  and  in  some  cases  with  marked  success,  and  these  will  now 
be  considered. 

In  the  fall  of  1900,  working  with  a  special  interrupter  enabling 
him  to  obtain  as  many  as  10,000  regular  sparks  per  second,  Fessenden 
succeeded  in  transmitting  speech  over  1  mile  (1.6  km.),  but  the  quality 
was  poor  and  there  was  much  noise.  By  1903  better  speech  was 


By  courtesy  of  Mr.  Bowden  Washington. 


Radio-Frequent  Spark  System  of  Ruhmer 


47 


obtained,  though  the  extra  noise  was  still  present,  It  does  not  appear 
that  Fessenden  developed  this  method  further,  although  he  describes  a 
special  rotary  gap  (with  40  per  cent,  platinum-iridium  studs)  operated 
on  5,000  volts  direct  current  and  arranged  to  give  20,000  sparks  per 
second  by  the  successive  charging  and  discharging  of  a  condenser. 

One  of  the  earlier  workers  with  radio-frequent  spark  systems  was 
Ernst  Ruhmer.  Ruhmer  used  as  his  gap  terminals  two  moving  metallic 
wires  which  passed  over  water  cooled  prismatic  surfaces  at  the  sparking 
point.  The  apparatus  is  shown  diagrammatically  in  Figure  35,  which 
shows  clearly  the  reels  on  which  the  moving  wire  is  wound  and  the 


FIGURE  36 — Ruhmer's   radiophone  transmitter. 

water-cooled  prismatic  gap  guides.  The  paramount  advantages  of 
Ruhmer- 's  arrangement  are  that  a  fresh  and  clean  surface  is  constantly 
presented  for  the  arc,  that  excellent  cooling  (and  consequently  quench- 
ing) is  obtained,  and  that  the  arc  length  should  remain  quite  constant. 
Ruhmer's  apparatus  is  shown  complete  in  a  hitherto  unpublished  photo- 
graph1* in  Figure  36.  The  arc  mechanism  is  shown  on  the  table  near 
the  extreme  right.  The  reels  from  and  to  which  the  wire  passes,  the 
driving  motor,  and  the  two  cup-shaped  containers  for  cooling' water  on 
the  top  of  the  apparatus  just  over  the  arc  are  visible.  These  cups  sur- 
mount the  gap  bearings.  At  the  right  end  of  the  table  are  the  con- 
trolling rheostats  and  lampboard  resistances  which  regulated  the  supply 
of  high  voltage  direct  current.  On  the  table  can  be  seen  the  micro- 


*  Which 
courtesy  of 


)hotograph,   together  with   a  number  of  others   shown   herein,   I  owe  to  the 
Ir.   William   Dubilier. 


48 


Spark  System  of  Dubilier 


phone  transmitter,  antenna  and  closed  circuit  ammeters,  coupling  and 
inductance  coils,  and  in  the  foreground  a  wave  meter. 

Another  early  system  (1911)  of  radio  telephony  with  what  the 
inventor,  Mr.  William  Dubilier,  called  a  "quenched  arc"  (really  a 
radio-frequent  spark)  transmitter,  is  indicated  in  outline  in  Figure  37. 
The  arc  is  indicated  at  A,  and  is  fed  with  moderately  high  tension  direct 
current.  Shunted  around  the  arc  is  the  oscillatory  circuit,  C  L17  which 
is  opened  automatically  by  a  simple  switch  during  reception.  The  oscil- 
latory circuit,  or  primary,  is  coupled  to  the  antenna  by  means  of  the  in- 
ductive coupling  between  L1  and  L2,  and  also  by  means  of  a  capacitive 
coupling  through  the  condensers  C^  and  C2.  Shunted  across  the  condenser 
0,2  is  the  telephone  relay  R  of  special  construction  to  be  described  here- 


w 


- — wwww- 


FIGUBE  37 — Dubilier  radiophone  transmitter  and  receiver. 

after.  It  is  practically  a  heavy  current  microphone  transmitter  coupled 
to  an  ordinary  receiver  electromagnet,  the  electromagnet  in  question  being 
energized  from  the  master  microphone  M.  Mr.  Dubilier  has  pointed  out 
that  the  terminals  of  an  ordinary  telephone  line  may  be  substituted  for 
the  local  microphone  connections  at  L,  L,  thus  causing  the  incoming 
energy  from  the  telephone  line  to  control  the  heavy  current  telephone 
relay,  R,  and  enabling  direct  communications  from  any  usual  land  line 
telephone  station  to  a  ship  at  sea. 

The  receiving  set  is  indicated  at  the  right  of  Figure  37,  and  is  an 
inductively-coupled,  aperiodic  secondary,  crystal  detector  receiver  of 
fairly  conventional  design. 

In  Figure  38  is  illustrated  a  complete  radiophone  station  of  this 
type.  The  box  at  the  left  of  the  table  contains  most  of  the  transmitting 
equipment.  On  the  right  rear  corner  of  the  top  of  the  box  is  the  multiple 


Spark  System  of  Dubilier 


49 


contact  commutator  for  changing  from  transmitting  to  receiving.  This 
commutator  performs  all  the  necessary  functions  indicated  by  the 
switches  in  Figure  37.  On  the  top  of  the  box  is  a  moderately  heavy 
current,  multiple  microphone  transmitter,  consisting  of  a  number  of 
transmitters  (7)  in  series.  At  the  right  of  the  box  is  mounted  the  special 
gap  or  discharger.  It  consists  of  one  heavy,  well  cooled  metal  electrode 
and  one  small  uncooled  electrode.  The  antenna  inductance  and  coupler 
is  shown  in  the  middle  of  the  table  and,  at  the  right  of  the  table,  the 
receiving  set. 

A  later  and  improved  type  of  set  is  shown  in  Figure  39,  which  is 


FIGUBE     38 — Dubilier     radiophone    trans- 
mitter and  receiver. 

the  entire  transmitter  self-contained.  The  antenna  commutating  switch 
has  been  somewhat  improved,  and  the  antenna  ammeter  is  mounted  on 
the  top  of  the  apparatus  box.  The  details  of  the  gap,  including  the 
horizontal  fins  for  air  cooling,  are  clearly  shown.  This  particular  set 
has  an  input  of  about  3  k.w.  and  has  enabled  radio  telephony  250  miles 
(400  km.)  on  one  occasion.  The  containing  box  is  only  14  inches  on  a 
side  35  cm.).  The  tilted  side  at  the  left  of  the  box  has  mounted  on  it 
one  of  the  spiral  coils  of  the  antenna  coupling,  so  that  merely  changing 
the  angle  of  inclination  of  the  exterior  tilted  side  varies  the  antenna-to- 
primary  coupling. 


50 


Spark  System  of  Lorenz  Company 


FIGURE  39 — Complete  Dubilier  radiophone 
transmitter. 


FIGURE  40 — Lorenz  Company  radiophone  transmitter. 


Lorenz  "Multitone"  System 


51 


FIGURE    41 — Lorenz    Company    aeroplane 
"multitone"  transmitter. 


The  C.  Lorenz  Company,  of  Berlin,  has  developed  through  its  engi- 
neer, Dr.  H.  Rein,  a  system  known  as  the  "multitone"  system.  Though 
primarily  intended  for  low  and  medium  power,  variable  tone,  radio  tele- 
graph transmitters  it  has  also  been  employed  in  radio  telephony.  The  cir- 
cuit diagram  of  the  set  is  given  in  Figure  40.  Here  G  is  a  moderately 
high  voltage  direct  current  generator,  R  and  X  are  feed  circuit  resistances 


FIGURE   42 — Interior   of    Scheller 
tone"  gap. 


'multi- 


and  choke  coils,  W  is  a  wave  changing  switch,  which,  after  a  preliminary 
and  final  adjustment  of  the  taps  on  L^  and  L2  enables  choosing  instan- 
taneously any  one  of  three  wave-lengths.  The  microphone  is  placed  in 
the  antenna  as  indicated.  Dr.  Rein  pointed  out  (as  had  also,  and  in- 
dependently, Dr.  Seibt)  that  the  resistance  of  the  microphone  for  best 
modulation  should  be  equal  to  the  total  resistance  of  the  remainder  of 


52 


Lorenz  Aeroplane  Set 


the  antenna  circuit.  This  would  imply  that  one-half  the  available 
energy  would  be  consumed  in  the  transmitter  microphones,  a  rule  that 
obviously  limits  the  available  modulated  output  of  sets  of  this  type. 
A  small  aeroplane  set  of  this  type  (intended  for  telegraphy,  how- 
ever), is  shown  in  Figure  41.  The  gap,  which  is  the  most  interesting 
portion  of  the  set,  is  seen  in  the  left  corner.  It  consists,  of  two  nearly 
concentric  spherical  segments,  one  fitting  within  the  other.  The  con- 
struction is  given  by  Figure  42,  which  is  the  dis-assembled  gap.  The 
discharge  takes  place  in  an  atmosphere  of  alcohol  vapor,  the  alcohol 
being  supplied  by  the  top  sight-feed  cup.  The  gap  was  devised  by 


FIGURE    43 — Lorenz    Company    "multitone" 
ship  set. 

Scheller.  A  complete  ship  station  of  this  type  is  given  in  Figure  43,  and 
a  semi-high-power  station  in  Figure  44.  This  last  has  gaps  for  high 
tension,  low  frequency  alternating  current,  the  gaps  being  assembled 
in  groups  of  six  in  series.  In  radio  telephony,  Rein  states  that  in 
general  carbon  grain  microphones  having  resistances  between  4  and  10 
ohms  were  used.  If  necessary,  these  were  coupled  to  the  antenna  through 
a  suitable  transformer,  or  otherwise,  in  such  fashion  that  the  equivalent 
resistance  they  interposed  in  the  antenna  circuit  was  equal  to  the 
remaining  antenna  resistance. 

Another  system  of  radio  telegraphy  that  has  been  adapted  to  radio 
telephony  in  quite  a  similar  manner  to  the  latest  mentioned  is  that  due 


Spark  System  of  von  Lepel 


53 


to  E.  von  Lepel.  The  circuit  used  is  identical  with  that  of  Figure  40  in 
some  cases,  though  in  the  recent  2  k.w.  sets  the  circuit  shown  in  Figure  42 
is  used.  This  is  analogous  in  action  to  that  shown  in  Figure  11  (but 
with  L,  Rlt  and  C\  omitted),  and  operates  in  the  manner  there  explained, 
at  least  to  some  extent.  The  spark  gap  shunt  circuit  L^C^  is  tuned  to 
nearly  the  same  frequency  as  the  plain  antenna  circuit. 

The  Lepel  gap  consists  of  a  plane  bronze  negative  electrode  separ- 


FIGURE    44 — Lorenz    Company    "multitone" 
semi-high  power  set. 


ated  from  a  plane  copper  positive  electrode  by  a  thin  sheet  of  "bond" 
paper,  say  0.002  inch  (0.05  mm.)  thick.  The  center  of  the  paper  sheet 
is  perforated,  and  when  approximately  500  or  600  volts  direct  current 
is  applied  between  the  electrodes,  the  discharge  bridges  the  gap.  It 
then  continues  rambling  outward,  slowly  burning  up  the  paper  sheet, 
in  a  spiral  path  starting  at  the  center  and  ending  at  the  edges.  This 
action  is  probably  due  to  the  deflecting  action  of  the  electrostatic  field 
between  the  plates  on  the  discharge  current.  Another  circuit  used  by 
von  Lepel  is  shown  in  Figure  45. 


54 


Spark  System  of  von  Lepel 


The  Lepel  gap  is  usually 
shunted  by  an  audio  frequency 
oscillating  or  "tone"  circuit,  when 
used  for  telegraphy.  When  used 
for  telephony,  however,  the  gap  is 
unshunted  and  a  very  rapid  suc- 
cession of  discharges  occur,  each 
setting  up  its  train  of  waves  in  the 
antenna,  as  indicated  in  Figure  32. 
In  the  receiver  there  is  then  heard 
a  faint  hissing  sound.  By  inserting- 
a  microphone  in  the  antenna,  this 
hissing  is  drowned  out  by  the  speech, 
and  telephony  becomes  possible.  A 
Lepel  radio  telegraph  set  (at  Har- 
fleur,  France),  is  shown  in  Figure 
46.  The  spark  gap,  which  is  water- 
cooled,  is  seen  just  to  the  left  of  the 
large  coupler.  It  can  easily  be  dis-assembled  for  cleaning  and  replace- 
ment of  the  paper  separator. 


FIGURE  45 — Lepel  transmitter. 


FIGURE  46 — Lepel  station  at  Harfleur. 


Spark  System  of  Chaffee 


55 


Continuing  our  discussion  of  radio  telephony  by  means  of  radio-fre- 
quent spark  transmitters,  we  consider  next  a  system  developed  by  Dr. 
E.  Leon  Chaffee  in  conjunction  with  Professor  George  "W.  Pierce.  This 
system  will  be  found  to  be  unique  in  certain  respects. 

The  wiring  diagram  of  the  transmitter  is  shown  in  its  essentials 
in  Figure  47,  and  presents  no  unusual  features.  The  direct  current 
generator  supplies  500  volts  (and  from  0.3  to  0.8  ampere;  i.  e.,  from 
150  to  400  watts)  per  gap.  The  resistance  provided  in  the  supply 
circuit  is  made  in  two  parts,  in  series,  one  roughly  variable  in  consider- 
able steps  and  the  other  smoothly  and  continuously  variable.  This  is 
desirable,  since  the  operation  of  the  gap,  though  steady,  depends  on 
a  proper  choice  of  the  current,  this  current  partly  determining  the 


FIGURE  47 — Chaffee  radiophone  transmitter. 


inverse  charge  frequency.  The  phenomenon  of  an  inverse  charge  fre- 
quency (that  is,  a  whole-number  ratio  between  the  secondary  oscillation 
frequency  and  the  primary  impulse  frequency)  has  been  treated  above, 
and  is  illustrated  in  Figure  33.  It  constitutes  a  distinctive  feature 
of  the  Chaffee  gap,  and  depends  on  the  intrinsically  great  damping 
in  the  gap. 

The  primary  condenser ..  C  need  not  be,  a  high  tension  condenser 
with  the  usual  low  power  sets,  and  generally  has  a  value  in  the  neighbor- 
hood of  0.009  microfarad.  The  coupling  between  ii:'and  L2  is  close. 
Ordinarily,  the  microphone  M  is  an  ordinary  Bell  transmitter,  though 
Chaffee  has  stated  that  this  type  of  microphone  deteriorates  somewhat 
under  radio  frequency  currents  of  one  ampere  or  more. 


56 


Chaffee  Spark  Gap 


The  cross  section  of  a  Chaffee  gap,  constructed  by  Messrs.  Cutting 
and  Washington  (under  patent  license  from  Dr.  Chaffee)  is  shown  in 
Figure  48.  The  gap  consists  of  plugs  of  aluminum  and  copper  respec- 
tively, one  or  two  square  centimeters  (or  roughly  two  or  four-tenths  of 


FIGURE  48 — Cross   section  of  Chaffee  gap.    Designed 
by  Cutting  and  Washington. 


a  square  inch)  in  area,  larger  dimensions  being  undesirable  in  the  sta- 
tionary forms  of  the  gap.  Originally  the  gap  was  run  in  an  atmosphere 
of  moist  hydrogen;  but  hydrogen  being  difficult  to  obtain  in  ordinary 
practice,  it  was  found  by  Cutting  and  Washington  that  alcohol  vapor 
could  be  substituted  provided  it  was  distilled  into  the  gap,  by  the  gap 
heat,  from  a  wick  entering  the  bottom  of  the  gap  chamber.  The  form 


FIGURE  49 — Chaffee  gap.   Designed  by  Cut- 
ting and  Washington. 


Chaffee  Radio-Frequent  Spark 


57 


of  gap  shown  is  made  air-tight  by  the  use  of  the  flexible  phosphor 
bronze  diaphragm,  A,  which  is  held  in  place  against  a  soft  rubber  gasket 
by  a  brass  ring.  Such  a  diaphragm  permits  the  necessary  movement 
required  in  adjustment  of  the  gap  electrode  separation.  The  external 
appearance  of  the  gap  with  its  adjusting  handle  and  cooling  fins  is 
given  in  Figure  49.  For  larger  powers,  a  still  later  modification  of  the 
gap  is  used  wherein  the  discharges  pass  between  a  rapidly  rotating 
aluminum  disc  and  a  stationary  copper  plate,  in  hydrocarbon  vapor. 
High  efficiency  (up  to  60  or  70  per  cent.)  can  be  obtained  with  these 
last  gaps. 

The  discharge  begins  when  the  switch  is  closed,  provided  the  dis- 
tance between  the  electrodes  is  not  over  0.1  mm.  (0.004  inch).  It  is 
a  noiseless  and  fixed  arc  of  a  vivid  violet  or  purple  color.  Occasionally 


FIGURE  50^  Aeroplane  set  with  Chaffee  gap.   Designed 
by  Cutting  and  Washington. 

moves  to  a  fresh  point  on  the  electrodes.  The  explanation  of  the 
extreme  quenching  action  lies,  according  to  Chaffee,  in  "the  practically 
instantaneous  re-establishment  of  the  high  initial  gap  resistance  when 
the  current  becomes  zero,  due  probably  to  the  formation  of  an  insulating 
oxid  film  on  the  aluminum ;  the  high  cathode  drop  of  the  anode  metal ; 
and  the  absorption  of  energy  by  the  secondary,  although  rectification 
usually  takes  place  without  this  aid."  The  best  operating  gap  lengths 
are  from  0.04  to  0.09  mm.  (0.0016  to  0.0036  inch). 

The  primary  discharge  is  a  half  loop  of  current,  and,  as  correctly 
indicated  in  Figure  33,  is  not  half  a  sine  wave.  Its  duration  does  not 
depend  on  the  primary  supply  current,  which  latter  affects  only  the 
'time  between  successive  primary  discharges.  The  time  between  suc- 
cessive primary  discharges  is  also  dependent  on  the  primary  capacity, 
since  the  charging  phenomena  connected  therewith  largely  determine  the 


58 


Syntony  to  Wave  Form 


successive  breakdowns  of  the  gap.  For  an  inverse  charge  frequency  of  2 
or  3,  the  secondary  oscillations  differ  only  imperceptibly  from  truly  sus- 
tained oscillation,  as  is  evidenced  by  the  interesting  fact  that  when  re- 
ceived on  a  normal  beat  receiver,  a  clear  musical  beat  tone  is  obtained. 
It  is  worthy  of  note  that  even  with  this  absolutely  aperiodic  primary 
discharge,  a  definite  relation  between  the  primary  period  and  the  second- 
ary period  is  required  for  maximum  secondary  response.  This  relation 
is,  however,  far  from  being  one  of  even  approximate  equality  being,  in 
fact,  a  ratio  of  1.71  for  primary  period  divided  by  secondary  period. 


FIGURE  51 — Front  view,  0.25  k.w.  Chaffee 

gap  set.    Designed  by  putting  and 

Washington. 

The  radio  frequency  output  per  gap  is  about  50  watts,  and  the 
efficiency  is  given  as  between  30  and  40  per  cent.  Two  or  three  gaps 
may  be  operated  in  series  on  500  volts,  and  four  gaps  on  1,000  volts. 
The  actual  voltage  drop  across  the  individual  gap  is  about  150  volts. 

The  Chaffee  apparatus  as  developed  for  commercial  work  by  Cut- 
ting and  Washington  is  illustrated  in  Figures  50,  51,  and  52.  The 
first  of  these  is  a  150-watt  aeroplane  set,  with  the  special  gap  in  the 
center.  The  primary  condenser  is  behind  the  gap,  and  the  primary-to- 
antenna  coupler  is  mounted  to  the  left.  In  the  latter  two  figures,  a  some- 
what larger  set  is  depicted.  Here  two  gaps  in  series  are  used,  and  a 
variometer  type  of  coupling.  Telegraphic  communication  was  main- 


Cutting  and  Washington-Chaffee  Sets 


59 


tained  with  one  of  these  sets  78  miles  (125  km.)  with  1.5  amperes  in 
the  antenna  at  480  meters  wave-length.  It  should  be  noted  that,  in 
marked  contrast  to  almost  all  sustained  wave  generators,  the  Chaffee  arc 
drops  but  slightly  in  output  at  very  short  wave-lengths. 

It  has  been  pointed  out  elsewhere  by  the  Author  that  a  marked 
tendency  exists  in  radio  development  toward  having  all  stations  operate 
with  sustained  radiation.  This  tendency  is  much  to  be  encouraged  be- 
cause of  the  remarkable  possibilities  in  the  direction  of  selectivity  with 
beat  reception  at  the  short  wave-lengths.  While  beat  reception  is  not  par- 
ticularly suited  to  radiophone  work,  it  is  to  be  hoped  that  ship  and 


FIGURE  52 — Side  view,  0.25  k.w.  Chaffee 

gap  set.     Designed  by  Cutting  and 

Washington. 

small  shore  stations,  and  all  amateur  stations  will  at  least  employ 
sustained  wave  generators.  If  this  is  done,  the  Chaffee  arc  would  seem 
to  be  a  suitable  device,  and  has  marked  possibilities. 

In  the  radiophone  experiments  described  by  Chaffee,  great  sim- 
plicity of  apparatus  was  achieved.  The  regular  tests  were  carried  on 
over  a  distance  of  one  mile  (1.6  km.).  A  single  gap  was  used  with 
from  0.2  to  0.5  ampere  through  it.  The  voltages  at  all  portions  of 
the  set  in  the  station  were  comparatively  low,  say  under  1,000  volts. 
It  is  stated  that  when  the  receiving  station  was  properly  tuned,  only 
a  slight  hum  or  hiss  was  heard  in  the  receivers,  which  was  tuned  out, 
if  desired,  and  in  any  case  drowned  by  the  voice.  The  articulation 


60  Spark  System  of  Ditcham 

was  very  good,  and  communication  was  maintained  for  hours  without 
losing  a  wor(J  or  making  any  adjustments. 

The  speech  was  heard  at  a  distance  of  40  miles  (64  km.),  but  it 
is  believed  that  this  distance  is  by  no  means  the  limit  of  the  system, 
even  when  only  one  gap  is  used. 

Mr.  Washington  has  informed  the  Author  that  using  two  gaps 
and  an  antenna  current  of  2.7  amperes  modulated.' by  a  water-cooled 


FIGURE    53 — Ditcham    radiophone    transmitter    and 
receiver. 

transmitter,  music  from  a  phonograph  was  clearly  distinguishable  on 
shipboard  at  a  distance  of  110  miles  (180  km.). 

Another  system  of  somewhat  similar  characteristics  was  developed 
by  Lieutenant  W.  T.  Ditcham  in  1912,  and  presents  some  features 
of  interest.  There  was  used  a  gap,  the  cathode  of  which  was  aluminum, 
hard  copper,  or  bronze,  the  anode  copper  or  steel,  each  electrode  about 
1  cm.  (0.4  inch)  in  diameter,  and  the  discharge  taking  place  in  an 


Spark  System  of  Ditcham 


61 


atmosphere  of  carbon  dioxid  under  pressure.  Four  such  gaps  were 
used  in  series,  at  a  voltage  of  1,000  and  a  current  of  1.5  amperes.  The 
capacity  in  the  primary  oscillating  circuit  was  0.012  microfarad. 

The  description  of  the  apparatus  given  by  the  inventor  makes  it 
clear  that  he  was  aware  of  the  advantage  of  securing  an  integral  in- 
verse charge  frequency,  and  attempted  to  secure  this  advantage  in 
designing  the  apparatus. 

The  antenna  fundamental  was  460  meters,  and  its  capacity  0.0007 
microfarad.  It  was  normally  used  at  550  meters  with  an  antenna 
current  of  8  amperes.  The  antenna  was  lower -than  desirable,  and  prob- 
ably had  only  small  true  radiation  resistance.  The  normal  distance  of 
communication  was  from  Letchworth  to  Northampton,  a  distance  of 
55  km.  (34  miles).  However,  signals  have  been  received  175  km. 
(110.  miles)  over  land.  In  reception,  a  crystal  detector  (namely, 
Pickard's  silicon-arsenic  combination)  was  used. 


1/WWWW\r 


f 


FIGURE  54 — T.  Y.  K.  radiophone  transmitter. 

It  is  interesting  to  note  that  the  maximum  radiation  was  attained 
in  the  system  when  the  primary  was  tuned  to  830  meters  and  the  an- 
tenna to  550  meters,  a  ratio  of  1.51  between  them.  This  ratio  is  not 
far  from  1.71,  the  value  found  by  Chaffee  for  most  efficient  operation. 
Coupling  to  antenna  as  high  as  40  per  cent,  is  used. 

We  are  indebted  to  Lieutenant  Ditcham  for  important  previously 
unpublished  data  on  the  operation  of  these  gaps.  With  hard  copper  or 
bronze  electrodes  in  carbon  dioxid  under  pressure,  the  gas  apparently 
had  two  functions:  (a)  cooling  by  expansion;  (b)  the  formation  of  a 
hard  crystalline  film  on  the  electrodes.  This  film  permitted  actual  con- 
tact of  the  electrodes  without  "short-circuiting"  or  arcing.  When  the 
film  was  once  formed,  the  gas  could  be  shut  off,  and  the  spark  would 
continue  active  for  five  or  ten  minutes  before  an  arc  started. 

The  entire  transmitter  is  given  by  Figure  53.  On  the  top  shelf 
are  mounted  the  four  series  gaps.  On  the  shelf  below  are  seen  tun- 


62 


Spark  System  of  Torikata,  Yokoyama,  and  Kitamura 


ing  inductances  and  a  relay,  while  on  the  bottom  shelf  is  mounted  the 
receiver  and  a  call-bell  system.  This  last  consisted  of  a  Brown  telephone 
relay  fed  from  the  crystal  detector  and,  in  its  turn,  supplying  the  cur- 
rent for  a  moving  coil  relay  of  no  great  sensitiveness.  A  long  musical 
dash  is  sent  for  calling,  the  pitch  being  regulable  by  variation  of  the 
speed  of  the  rotary  make-and-break  device  ("chopper")  which  is  in- 
serted in  the  coupling  between  the  closed  and  antenna  circuits,  A 


FIGURE  55 — Front  view  of  T.  Y.  K.  radio- 
phone transmitter  and  receiver. 

selective  method  of  calling,  permitting  ringing  any  one  of  a  number 
of  stations  within  a  given  zone  was  experimented  with,  but  no  details 
are  available  as  to  its  success  in  operation. 

A  system  of  radio-frequent  spark  telephony  has  been  devised  by 
Messrs.  Wichi  Torikata,  E.  Tokoyama,  and  M.  Kitamura.  The  spark 
or  arc  terminals  in  this  system  are  composed  of  magnetite  (oxid  of  iron) 
and  brass.  Other  alternatives  are  aluminum  <  ilicon,  ferro-silicon,  car- 


T.  Y.  K.  Spark  Radiophone 


63 


borundum,  or  boron  against  minerals  such  as  graphite,  meteorite,  iron 
or  copper  pyrites,  bornite,  molybdenite,  marcasite,  or  others.  Usually 
the  electrodes  are  of  small  surface,  this  being  regarded  as  essential  by 
the  inventors.  The  power  supplied  per  gap  is  500  volts  and  0.2 
ampere.  A  capacity  of  approximately  0.05  microfarad  is  used  in  the 
primary  oscillating  circuit.  About  1  ampere  is  modulated  in  the  antenna 
by  the  microphone,  and  the  every-day  range  is  given  as  10  to  15  miles 
(25  km.).  Ordinary  crystal  detector  reception  is  employed. 

The  wiring  diagram  of  the  apparatus  is  given  in  Figure  54.  It 
will  be  seen  that  the  starting  device  is  of  an  unusual  nature.  It  seems 
that  a  high-resistance  film  forms  on  the  surface  of  the  electrodes,  as  in 


FIGURE  56 — Equilibrator  and  spark  gaps  of 
T.  Y.  K.  radiophone  transmitter. 


jieutenant  Ditcham's  system,  and  it  is  necessary  in  consequence  to 
have  some  means  of  obtaining  a  momentary  high  voltage  to  break  down 
this  surface  film,  and  start  the  discharge.  This  is  accomplished  by 
having  a  steady  current  flowing  normally  (before  oscillations  are  de- 
sired) in  the  inductance  V  as  indicated,  this  current  being  quickly  broken 
at  Q  when  it  has  once  fairly  started.  The  gap  electrodes  being  in 
contact,  the  high  inductive  voltage  breaks  down  the  surface  film,  and 
the  armature  P  draws  the  electrodes  apart  and  serves  as  a  sort  of  auto- 
matic arc  length  regulator  thereafter. 

Figure  55  illustrates  the  transmitter  proper  and  receiver.  A  nor- 
mal heavy-current  microphone  transmitter  is  used  (mounted  at  the 
top  in  front  of  the  eqvUbrator).  The  primary  oscillating  circuit, 


64 


T.  Y.  K.  Spark  Radiophone 


FIGURE   58 — 100-to-500-volt   direct  current 
coils  for  direct  current  supply  circuit 
of  T.  Y.  K.  radiophone  transmitter. 

capacity  control  switch  is  directly  below  the  microphone.  The  receiver 
is  mounted  in  the  lower  case,  together  with  the  "sending-to-receiving" 
switch.  The  crystal  detector  is  enclosed  in  a  metal  housing,  the  door 
of  which  appears  at  the  lower  left  side  of  the  receiving  apparatus  case. 
A  usual  test  buzzer  and  normal  tuning  and  coupling  coil  switches  are 
provided.  The  equilibrator  is  shown  in  Figure  56,  with  the  alternative 
spark  gaps  (aluminum-brass  or  aluminum-magnetite),  at  the  lower  left 
corner.  A  small  lamp  with  cover  is  mounted  at  the  rear  to  indicate 


FIGURE  58 — 100-to-500  volt  direct  current 

rotary  converter  of  T.  Y.  K. 

radiophone  transmitter. 


Spark  Radiophone  of  Hanscom 


65 


antenna  current.  The  lamp  resistance  and  choke  coil  box  for  the  high 
voltage  generator,  supply  circuit  to  the  gap  appear  in  Figure  57. 
The  100  volt  (and  2.7  ampere)  to  500  volt  (and  0.2  ampere)  rotary 
converter  is  illustrated  in  Figure  58. 

In  June,  1913,  there  were  established  eight  land  stations  of  this 
type  in  Japan  and  seven  stations  were  installed  on  board  ship.  It  is 
stated  that  commercial  service  was  initiated  at  this  early  date. 

A  type  of  oscillator  due  to  Mr.  W.  W.  Hanscom,  operates  with  the 
gap  surfaces  immersed  in  alcohol.  Their  separation  is  automatically 


FIGUKE    59 — One-half    kilowatt    Hanscom 
radiophone  transmitter. 

regulated  by  an  electro-magnet  plunger,  a  gravity  adjustment  by  means 
of  a  sliding  weight  being  provided  for  initial  installation.  The  gap 
voltage  is  low  (of  the  order  of  100  volts).  It  is  stated  that  steady 
automatic  operation  for  hours  has  been  secured.  Only  an  occasional 
supply  of  alcohol  and  infrequent  renewal  of  the  gap  surfaces  are 
required. 

In  Figure  59  is  shown  such  a  set.  The  gap  and  regulator  are 
mounted  to  the  rear  of  the  panel.  The  electromagnet  winding  is  also 
used  as  a  choke  coil  in  the  supply  circuit.  Direct  current  at  voltages 
from  110  to  500  is  supplied,  and  currents  from  5  to  8  amperes  pass 


66 


Spark  Direct  Current  System  of  de  Forest 


I VWVWVWA    I— fl 

A  D.C 


I 

T 


-II- 


FIGURE   60 — de   Forest   radiophone   transmitter — 
D.  C.  type. 


through  the  gap.  The  system  has  been  operated  on  wave-lengths  between 
300  and  2,700  meters.  For  modulation,  a  water-cooled  microphone 
transmitter  carrying  2.5  amperes  is  used. 

"With  vacuum  valve  reception,  distances  of  100  miles  (160  km.) 
are  covered,  but  it  is  claimed  that  distances  of  260  miles  (400  km.)  are 
occasionally  bridged.  On  one  occasion,  the  800-mile  (1,300  km.)  span 
from  San  Francisco  to  Seattle  was  covered. 

Dr.  Lee  de  Forest  has  done  considerable  work  in  connection  with 
radio  telephony.  Originally  he  worked  with  a  small  arc  of  the  Poulsen 
type,  and  communication  over  short  ranges  was  obtained.  More  recently 


FIGURE  61 — de  Forest  D.  C.    radiophone  transmitter. 


Spark  Direct  Current  System  of  de  Forest 


67 


he  has  worked  with  several  types  of  radio-frequent  spark  radiophone 
transmitters,  and  two  of  these  types  will  be  here  described. 

The  first  of  these  is  a  moderately  high  voltage,  direct  current 
system.  The  wiring  diagram  is  given  in  Figure  60.  As  will  be  seen, 
a  1,000-volt,  direct-current  generator  supplied  a  two-section  quenching 
gap  through  a  regulating  resistance  and  choke  coil.  The  gap  itself  is 
made  of  parallel  studs  of  tungsten  in  air,  with  minute  but  regulable  sep- 
aration. Shunted  around  the  gap  is  an  oscillating  circuit  which  is 
directly  coupled  to  the  antenna.  Two  heavy  current  microphones 


FIGURE  62 — de  Forest  portable  radiophone  set. 


>metimes  air  cooled  by  a  blower)  are  connected  in  series  in  the  ground 
id  of  the  antenna.  A  small  set  of  this  type  is  shown  in  Figure  61. 
It  differs  from  that  just  described  in  that  only  one  gap  section  is 
used  and  a  single  microphone  in  the  antenna.  The  antenna  ammeter 
is  shown  mounted  on  the  upper  left-hand  portion  of  the  apparatus  box 
which  contains  the  primary  condenser,  inductances,  choke  coils,  and 
antenna  switch.  This  sending-to-receiving  transfer  switch  is  controlled 
by  the  projecting  knob  on  the  upper  right-hand  portion  of  the  appar- 
atus box.  The  small  600-volt  generator  is  shown  separately.  A  0.25-h.p. 
(200-watt)  motor  is  recommended  for  driving  the  generator.  The 


68 


Spark  Alternating  Current  System  of  de  Forest 


range  is  given  as  from  7  to  15  miles   (10  to  25  km.).     The  set,   as 
designed,  operates  at  wave-length  from  400  to  1,000  meters. 

A  portable  type  of  radiophone  is  shown,  set  up,  in  Figure  62.  It 
will  be  seen  that  the  double  microphone  transmitter  is  used  in  the 
set  in  question.  The  receiving  set  is  seen  at  the  left  and  toward  the 
back  of  the  instrument  case.  A  somewhat  larger  set  is  illustrated  in 
Figure  63,  with  an  air-cooled,  two-section  gap.  The  antenna  switch 
and  direct  coupling  coil  are  mounted  to  the  right  of  the  panel.  When 
used  for  radio  telephony,  an  air-cooled,  twin-microphone  transmitter  is 
mounted  on  the  panel,  usually  under  the  supply  circuit  ammeter. 


FIGURE  63 — de  Forest  2  k.w.  radiophone  panel 
transmitter. 


An  alternating  current  system  of  spark  radio  telephony  has  been 
developed  by  de  Forest.  The  circuit  diagram  is  given  in  Figure  64. 
G  is  a  3,000-cycle  alternator  which  supplies  current  to  the  primary 
of  the  transformer  through  the  tuning  condenser  indicated,  this  latter 
having  a  value  of  approximately  8  microfarads.  The  transformer 
raises  the  terminal  voltage  from  100  to  5,000  volts.  A  number  of  gap 
sections  similar  to  those  previously  described  are  used,  and  the  primary 
is  inductively  coupled  to  the  antenna.  A  double  microphone  is  used  in 
the  ground  lead  as  before.  The  audio  frequency  tuning  to  3,000  cycles 
in  the  supply  circuit  is  of  interest.  No  data  is  available  as  to  the 
extent  to  which  the  3,000  cycle  note  can  be  eliminated  and  prevented 


Spark  Alternating  Current  System  of  de  Forest 


69 


from  interfering  with  the  speech  in  the  arrangement  under  considera- 
tion. It  is  likely,  however,  that  a  square  generator-wave  form  would  be 
of  assistance  in  this  connection. 

When  it  is  attempted  to  receive  signals  from  the  de  Forest  radio- 
phone transmitters  by  ordinary  beat  reception,  (no  speech  being  trans- 
mitted) a  very  poor  note  almost  without  musical  characteristics  is  ob- 
tained. This  is  accounted  for  by  the  absence  of  a  definite  inverse  charge 
frequency  and  the  consequent  extremely  frequent  alterations  in  phase 
of  the  radiated  energy. 


T 


FIGURE  64 — de  Forest  radiophone  transmitter — A.  C.  type. 


A  1-k.w.,  direct-current  equipment  placed  on  a  train  of  the  Dela- 
ware, Lackawanna,  and  Western  Railroad  permitted  communication  from 
Scranton  to  a  moving1  express  train  at  full  speed  up  to  53  miles 
(85  km.).  De  Forest  gives  some  interesting  figures  as  to  the  average 
range  of  the  sets.  For  the  2-k.w.  set,  using  masts  100  feet  (30  m.) 
high  and  at  least  50  feet  (15  m.)  apart,  the  range  over  sea  is  up  to 
100  miles  (160  km.)  and  over  land  up  to  75  miles  .(120  km.).  If 
40-foot  (13  m.) masts  are  used,  these  ranges  are  reduced  to  0.3  or  0.4 
of  the  values  given.  For  the  5-k.w.  sets,  with  similar  200-foot  (60  m.) 
masts  at  least  100  feet  (30  m.)  apart,  the  sea  range  is  up  to  400  miles 
(640  km.)  and  the  land  range  up  to  300  miles  (480  km.).  This  range 
is  reduced  to  one-half  the  values  given  if  the  masts  are  reduced  in 
height  to  100  feet  (30  m.).  It  is  further  stated  that  over  heavily 
wooded  and  mountainous  country,  the  ranges  may  be  reduced  25  or 
even  50  per  cent. 


70 


Radio  Frequent  Spark  System  of  Moretti 


FIGURE  65 — Diagrammatic  rep- 
resentation of  Moretti  arc. 


Excellent  results  have  been  obtained 
with  a  recent  method  of  radio-frequent 
spark  type  using  the  Moretti  * '  arc. ' '  The 
Moretti  arc  seems  to  be  the  most  powerful 
generator  of  this  sort  yet  discovered.  It 
is  a  simple  device,  being  shown  in  Figure 
65.  In  the  figure,  the  arc  is  shown  en- 
closed in  an  air-tight  box  of  insulating 
material,  but  this  enclosure  is  not  es- 
sential. The  arc  may  be  used  in  the  open 
air.  Both  electrodes  are  of  massive  cop- 
per, one  with  a  plane  surface  and  the  other  A  with  a  longitudinal  per- 
foration through  which  is  pumped  a  steady  stream  of  acidulated  water. 
This  jet  impinges  on  the  upper  electrode  (which  is  the  negative  one, 
usually)  ;  and  the  velocity  of  the  stream  of  water  can  be  suitably  regu- 
lated by  a  valve  placed  in  the  feed  pipe.  The  theory  of  its  action,  as 
given  by  Professor  Vanni,  makes  it  a  device  somewhat  analogous  to  the 
usual  Wehnelt  interrupter.  He  suggests  that  at  the  moment  of  forma- 
tion of  the  arc,  the  water  passes  into  the  spheroidal  state,  vaporizing 
rapidly,  and  thus  breaks  the  circuit  very  suddenly.  At  the  same  instant, 
the  water  is  partly  dissociated  into  hydrogen  and  oxygen ;  which,  being 
an  explosive  mixture,  quickly  recombines,  whereupon  the  entire  cycle 
is  repeated. 


FIGUBE  66 — Scheidt-Boon  Moretti  arc  as  used  at 
Laeken  station  of  Mr.  Robert  Goldschmidt. 


Vanni  and  Bethenod's  Modified  Moretti  "Arc" 


71 


Whatever  the  action,  the  effect  is  to  open  the  arc  circuit  at  a  radio 
frequency,  which  fact  can  be  verified  by  an  examination  of  the  arc  by  a 
rotating  mirror  oscillograph.  The  spark  frequency  is  thus  found  to 
be  several  hundred  thousand  per  second.  As  in  the  Chaffee  arc,  the 
impulses  are  stated  to  be  unidirectional,  though  whether  an  inverse 
charge  frequency  exists  and  whether  syntony  to  wave  form  is  evidenced 
is  not  indicated  in  the  published  descriptions. 

This  arc  has  been  improved  in  construction  by  Mr.  Bethenod  in 
that  a  precision  regulator  of  the  arc  length  has  been  designed  by  him, 
and  that  a  special  direct  current  generator  has  been  used  of  high  no-load 
e.m.f .  and  markedly  lower  load  voltage.  In  this  way,  the  series  resistance 
in  the  supply  circuit  can  be  avoided  and  better  efficiency  attained. 


FIGURE   67 — Laeken    (Brussels)    station   of  Mr.   Robert  Gold- 
schmidt,  showing  Moretti  arc  and  Marzi  microphone. 

As  normally  used,  the  arc  is  placed  in  series  with  resistance  and 
inductance  across  the  terminals  of  a  600-volt  direct  current  generator. 
The  energy  supply  in  the  following  experiments  carried  on  by  Professor 
Vanni  was  1  kilowatt.  Across  the  arc  is  placed  a  usual  oscillatory  cir- 
cuit, which  is  inductively  coupled  to  the  antenna.  In  the  antenna  was 
placed  Vanni 's  special  hydraulic  microphone  transmitter  to  be  described 
hereafter.  Unquestionably,  the  remarkable  results  obtained  are  in  large 
part  to  be  ascribed  to  the  development  of  this  unusual  form  of  telephone 
transmitter.  The  antenna  current  secured  was  12  amperes. 


72      Spark  Radiophone  Experiments  of  Vanni  and  Goldschmidt 

In  1912,  experiments  were  carried  on  by  Vanni  from  the  station 
at  Cento  Celle,  several  kilometers  from  Rome.  The  Island  of  Ponza, 
120  km.  (75  miles),  away,  was  first  reached,  then  Magdalena,  160  km. 
(100  miles)  away;  then  Palermo,  420  km.  (260  miles)  away;  then 
Vittoria,  600  km.  (375  miles)  away,  and  finally  Tripoli,  no  less  than 
1,000  km.  (625  miles)  away.  The  results  are  noteworthy,  and  seem  to  be 
attainable  without  excessive  uncertainty,  as  evidenced  by  the  work  done 
by  Mr.  Goldschmidt  (of  Laeken,  near  Brussels,  in  Belgium),  and  by  the 
Marzi  brothers  in  Italy. 

The  experiments  carried  on  at  Laeken  early  in  1914,  before  the 
unfortunate  destruction  of  the  station  by  its  owners  to  prevent  it  from 
falling  into  the  hands  of  an  invading  army,  are  of  considerable  interest. 

As  generator,  a  modified  Moretti  arc  was  used,  fed  with  600  volts. 
It  is  shown  in  Figure  66*.  One  electrode  was  rotated  rapidly.  This 
was  the  positive  electrode  and  consisted  of  a  number  of  discs  mounted  on 
an  axle.  The  negative  electrode  consisted  of  the  surface  of  rods  held 
in  sleeves  with  screw  adjustment  so  that  the  arc  length  was  directly 
regulable.  As  stated  previously,  a  water  jet  was  injected  into  the  arc 
A  special  microphone  heavy-current  transmitter  devised  by  the  Marzi 
brothers  was  used,  and  this  will  be  considered  hereafter.  Several  Moretti 
arcs  in  series  have  been  used  by  the  Marzi  brothers.  With  four  arcs 
in  series,  running  at  2,400  volts,  radiophone  transmission  was  effected 
between  La  Spezzia  and  Messina,  the  full  length  of  Italy. 

The  equipment  used  in  the  Laeken  experiments  is  shown  in  Figure 
67.  On  the  center  of  the  table  is  mounted  the  Moretti  arc,  to  the  left 
of  which  are  seen  the  coupling  spirals.  In  the  upper  left-hand  portion 
of  the  picture  is  shown  the  heavy-current  transmitter,  which  is,  in  fact, 
controlled  by  the  small  transmitter  held  in  the  hand  of  the  experimenter. 

On  March  13,  1914,  using  3  amperes  in  the  antenna,  communication 
was  established  between  the  station  at  Laeken  and  the  Eiffel  Tower  in 
Paris,  a  distance  of  200  miles  (320  km.).  Tests  were  carried  on 
regularly  on  wave-lengths  of  300,  600,  800,  and  1,100  meters.  This  arc 
shows  the  usual  radio-frequent  spark  characteristic  of  satisfactory  opera- 
tion on  short  wave-lengths. 

Reception  was  accomplished  in  various  way,  but  it  is  interesting 
to  note  that  the  experimenters  give  the  following  as  the  order  of  merit 
of  detectors  in  radiophone  reception:  sensitive  crystals  (such  as  galena), 
the  audion,  the  Fleming  valve,  carborundum,  and  the  electrolytic 
detector. 


*  Figure  66  and  67  are  reproduced  by  permission  from  the  French  Journal  "T.  S.  F.," 
based  on  material  received  from  Mr.  Scheidt-Boon    of  Brussels   (1914). 


Radio  Frequent  Spark  System  of  Marconi 


73 


It  has  been  shown  in  connection  with  Figures  32  and  33,  that  a 
series  of  short,  highly  damped  currents  spaced  regularly  in  a  primary 
circuit  would  produce  what  was  practically  sustained  alternating  current 
of  radio  frequency  in  the  secondary  circuit  (page  45).  Suppose  then 
that  there  be  produced  in  a  number  of  primary  circuits  in  succession 
the  currents  shown  in  Figure  68  on  the  lines  marked  D^  D2,  D3,  and  D4. 

As  will  be  seen,  in  the  first  primary  circuit  there  are  regularly 
spaced,  highly  damped  wrave  trains.  In  the  second  primary,  there  are 
similar  currents,  but  these  occur  at  times  which  are  later  than  the 
first  primary  trains  by  one-quarter  of  the  time  between  trains.  Similarly, 


A 


FIGURE  68 — Production  of  Sustained  Radiation  by  Marconi  "Timed 
Spark''  Method. 

in  the  third  primary,  there  are  wave  trains  which  lag  behind  those  of 
the  first  primary  by  a  time  equal  to  two-quarters  of  the  time  between 
trains;  and  in  the  fourth  primary,  the  trains  lag  by  three-quarters  of 
the  time  between  trains  behind  those  of  the  first  primary.  The  current 
which  is  produced  in  the  common  secondary,  to  which  all  the  primaries 
are  coupled  is  shown  in  the  line  marked  A  in  the  figure.  It  is  clear  that 
after  the  first  few  periods,  the  secondary  current  will  have  practically 
constant  amplitude.  It  will  be  noticed  also  that  for  perfect  regularity 
in  secondary  current,  the  time  between  wave  trains  should  be  integ- 
rally related  to  the  radio  frequency  period  of  the  secondary  current. 
To  carry  out  this  idea,  Senatore  Marconi  has  devised  the  circuits 
shown  in  Figure  69.  The  first  primary  circuit  consists  of  the  rotary 
discharger  Dlt  the  condenser  Clt  and  the  inductance  Plt  The  second 
primary  circuit  consists  of  the  discharger  Z)2,  and  P.2  and  C2 ;  and  so  on. 


74 


Marconi's  "Timed  Spark"  System 


Each  of  the  dischargers  is  fed  with  direct  current  of  high  voltage  (e.g., 
at  10,000  volts)  by  the  generator  G.  The  antenna  circuit  (between  A 
and  G)  is  coupled  to  the  various  primaries  through  the  inductances 
8  &>  #  and  #. 


U<A    kpA  | 

T^rta-T 


KV1* 


CSS  1   CJ=±r     J    C,s±= 


mini 


FIGURE  69 — Marconi  "Timed  Spark"  Method  of  Producing  Sustained  Radiation. 

By  the  means  shown,  practically  sustained  radiation  is  obtained  in 
the  antenna  circuit.  It  will  be  noted  that  each  of  the  dischargers  is 
shifted  on  the  common  shaft  by  an  angular  distance  equal  to  one-quarter 
the  angular  distance  between  successive  studs  on  the  dischargers. 

A  later  modification  of  the  method  given  is  used  at  the  Carnarvon, 
Wales  high  power  station  of  the  Marconi  Company,  which  station  will 
work  with  a  corresponding  station  at  Marion,  Massachusetts.  It  is 


FIGURE  70 — Marconi  Company  "Timed  Spark"  Discharger. 


Marconi's  "Timed  Spark"  System 


75 


noticeable  in  receiving  Carnarvon  in  the  United  States,  by  beat  reception, 
that  pure  beat  tones  are  obtained;  thus  demonstrating  the  essentially 
constant  amplitude  and  frequency  of  the  radiated  waves.  The  multiple 
discharger  used  in  this  way  at  Carnarvon  is  illustrated  in  Figure  70. 
The  driving  motor  is  visible  at  the  right,  and  the  separate  "  trigger" 
dischargers  at  the  left.  Though  equipment  of  this  sort  has  not  been  used 
for  radio  telephony  up  to  the  present,  so  far  as  the  Author  is  aware, 
it  does  constitute  an  apparently  reliable  and  powerful  method  of  produc- 
ing the  requisite  sustained  radiation  and  may  be  applied  in  the  field 
mentioned  in  the  futurt. 


CHAPTER  IV. 

(c)  VACUUM  TUBE  OSCILLATORS;  DUSHMAN'S  DATA;  TEM- 
PERATURE AND  SPACE  CHARGE  LIMITATION  OF  PLATE  CUR- 
RENT; THERMIONIC  CURRENTS  IN  FILAMENT;  WHITE  FILA- 
MENT SUPPLY  METHOD  ;  GRID  POTENTIAL  CONTROL  OF  PLATE 
CURRENT  ;  TUBE  AMPLIFICATION  OF  ALTERNATING  CURRENT  ; 
SELF-EXCITED  OSCILLATIONS;  OSCILLATING  CIRCUIT  OF  MEIS- 
SNER;  MARCONI-FRANKLIN  CIRCUITS;  DE  FOREST  ULTRA- 
UDION  AND  OTHER  CIRCUITS  ;  HIGH  POWER  TUBES  ;  GENERAL 
ELECTRIC  COMPANY  PLIOTRONS;  OSCILLATING  CIRCUIT  OF 
GENERAL  ELECTRIC  COMPANY  ;  WESTERN  ELECTRIC  COMPANY 
TUBES;  EXPERIMENTS  OF  COLPITTS;  EXPERIMENTS  OF 
HEISING  ;  NICOLSON  TUBE  ;  GENERAL  ELECTRIC  COMPANY 
DYNATRON  AND  PLIODYNATRON  ;  HULL'S  DYNATRON  AMPLI- 
FIER AND  OSCILLATOR;  HULL'S  PLIODYNATRON  CONTROLLED 
OSCILLATOR. 

(c)  VACUUM  TUBE  OSCILLATORS. 

There  has  arisen  within  the  last  few  years  a  new  and  important 
type  of  sustained  radio  frequency  generator,  namely,  the  hot  cathode 
vacuum  rectifier,  usually  with  three  internal  electrodes.  As  will  appear, 
the  ease  and  certainty  of  control  of  currents  formed  by  pure  electron 
streams  in  a  vacuum  has  rendered  these  devices  suitable  not  only  for 
use  as  generators,  but  also  amenable  to  telephonic  modulation  and  con- 
trol of  the  radio  frequency  output.  In  the  following  discussion,  however, 
we  shall  consider  only  tube  construction  and  the  associated  circuits 
enabling  the  generation  of  radio  frequency  currents.  The  modulating 
methods  for  radio  telephonic  purposes  will  be  considered  together  with 
the  station  apparatus  under  a  later  heading. 

Since  the  mode  of  action  of  the  devices  described  here  is  still,  in 
many  cases,  under  judicial  consideration  in  the  courts  of  this  country, 
we  shall  confine  ourselves  to  giving  without  comment  the  explanations 
advanced  by  the  various  investigators. 

We  shall  consider  first  electron  currents  through  a  vacuum.  If 
the  filament  FF  in  Figure  71  is  heated  to  bright  incandescence  by  the 
filament  battery  FB  (regulated,  if  necessary,  by  a  series  rheostat  in  the 

76 


Thermionic  Currents 


77 


battery  circuit,  not  shown)  there  will  be  emitted  from  the  filament  a 
copious  stream  of  negative  electrons  that  is,  small  charges  of  negative 
electricity.  A  definite  number  of  these  are  emitted  from  the  filament 
per  second  for  each  centimeter  of  length  of  the  filament.  The  number 
emitted  depends  markedly  on  the  temperature,  increasing  extremely 
rapidly  as  the  higher  temperatures  are  attained.  For  example,  Dr. 
Saul  Dushman  of  the  General  Electric  Company,  found  that  the  current 
per  square  centimeter  of  filament  surface  increased  from  about  0.14 
ampere  per  sq.  cm.  at  2,300°  absolute  to  0.36  ampere  per  sq.  cm.  at 
2,400°.  The  values  for  2,500°  and  2,600°  were  respectively  0.89  and 
2.04  amperes  per  sq.  cm.  It  is  quite  obvious  that  the  highest  tempera- 
tures of  filament  consistent  with  not  burning  out  the  filament  and  a 
reasonably  long  filament  life  are  desirable  if  large  currents  are  to  be 
passed  through  the  tube. 


FIGURE  71 — Thermionic  currents. 

Suppose  that  the  cylindrical  metal  plate  be  placed  around  the 
filament  as  indicated  at  P.  Suppose  further  that  a  battery,  PB,  and 
galvanometer  G  be  connected  in  series  between  plate  and  filament.  If 
the  negative  side  of  the  battery  be  connected  to  the  plate,  practically  no 
current  will  flow  through  the  galvanometer.  If,  on  the  other  hand,  the 
positive  side  of  the  battery  be  connected  to  the  plate,  negative  electrons 
will  be  attracted  to  the  plate,  returning  to  the  filament  at  the  lower 
point,  F.  Using  the  ordinary  convention  for  the  direction  of  current 
flow  (which  is  opposite  to  the  direction  of  flow  of  the  electron  stream), 


78 


Thermionic  Current  Temperature  Limitation 


we  say  that  a  current  flows  from  the  plate  to  the  filament,  The  device 
is  therefore  a  rectifier,  since  it  permits  the  flow  of  current  from  plate 
to  filament,  but  not  vice  versa.  This  form  of  the  device  has  been  used 
by  Fleming  since  1906  as  a  detector  for  radio  receivers.  In  a  highly 
evacuated  form,  it  has  recently  been  developed  into  the  new  Coolidge 
X-ray  tube  and  the  so-called  "kenotron"  or  high  voltage,  high  vacuum 
rectifier  of  the  General  Electric  Company. 

The  current  through  such  a  device  in  the  plate  circuit  obviously 
depends  on  the  plate  potential.  In  general,  the  more  positive  the 
plate,  the  higher  the  electron  velocity  across  the  space  between  filament 
and  plate,  and  the  greater  the  plate  current.  There  is  however,  a  clear 
limitation  to  this  increase  of  current.  At  any  given  temperature,  only 


AMPERE5 

FIGURE  72 — Relation  between  voltage  and 

current  for  pure  electron  rectifier 

at  a  given  temperature. 

a  given  number  of  electrons  can  be  emitted  by  the  filament  per  second, 
and  when  all  of  these  are  drawn  to  the  plate  per  second,  no  increase 
in  plate  voltage  will  cause  an  increase  in  plate  current.  This  is  called 
the  temperature  limitation  of  plate  current.  In  Figure  72,  it  is  illus- 
trated at  B.  In  the  lower  portion  of  the  curve  the  current  increases 
(as  can  be  shown  by  mathematical  analysis)  with  the  three-halves 
power  of  the  applied  plate  voltage,  but  at  B  we  reach  the  limiting  cur- 
rent value  at  the  given  temperature  and  the  curve  bends  sharply  to  (7, 
whereafter  the  plate  current  remains  constant  unless  the  temperature  of 


Thermionic  Current  Space  Charge  Limitation 


79 


the  filament  is  raised.    In  the  portion  AB  of  the  curve,  the  current  from 
the  plate  to  filament  is  actually  given  by  the  equation : 


i=  14.65(10) 


,3/2 


where  is  the  current  in  amperes  in  the  plate  circuit,  I  is  the  length 
of  the  filament  in  centimeters,  and  r  the  radius  of  the  cylinder  in  centi- 
meters. The  curve  ADE  is  for  a  lower  temperature,  and  therefore  also 
for  a  lower  limiting  current. 

There  is  a  second  type  of  current  limitation  at  a  given  plate 
voltage  which  may  prove  very  serious  in  practice  in  high  vacuum 
tubes.  This  is  the  so-called  space  charge  limitation,  and  depends  on 


I 
u 


< 

UJ 
Q. 

E 

C 

UJ 

J 

s  —  -  —          D                    B 
/A 

-CURPENT- 

FIGURE    73 — Space    charge    limitation    of 

thermionic  current  at  a  given 

plate  voltage. 

the  following  considerations.  If  the  plate  voltage  has  a  given  value, 
increase  of  filament  temperature  will  increase  the  plate  current  to  a 
point  B,  but  not  further.  This  is  due  to  the  following  effect:  The 
cloud  of  negative  electrons  surrounding  the  filament  at  any  time  acts 
as  a  large  negative  charge  in  its  neighborhood,  and  consequently 
repels  all  electrons  which  are,  or  tend  to  be,  emitted  by  the  filament, 
thus  choking  back  the  electron  current  stream.  If  the  charge  in  the 
space  surrounding  the  filament  becomes  sufficiently  great,  no  increase 
in  temperature  at  a  given  voltage  will  produce  any  further  current. 
Either  the  plate  voltage  must  be  increased  or  the  bulb  construction 
altered  so  as  to  diminish  the  space  charge.  Bringing  the  plate  and 
filament  close  to  each  other  will  diminish  the  space  charge  effect.  The 
effect  is  indicated  at  B  in  Figure  73;  and,  for  a  lower  applied  plate 
voltage,  at  D  with  the  dashed  line. 


80 


Combined  Lighting  and  Thermionic  Currents 


In  considering  the  current-carrying  capacity  of  vacuum  tube  recti- 
fiers, Dr.  Dushman  gives  data  as  to  the  current  in  milliamperes  per 
centimeter  of  filament  length  at  a  safe  working  filament  temperature. 
Thus  with  a  filament  0.005  inch  (0.012  cm.)  in  diameter,  0.030  ampere 
can  be  safely  emitted  per  centimeter  of  length.  Under  such  condi- 
tions, the  filament  heating  current  will  represent  3.1  watts  of  power 
per  centimeter  of  length.  For  a  filament  0.01  inch  (0.025  cm.)  in 
diameter,  these  figures  become  respectively  0.10  ampere  and  7.2  watts 
per  unit  length.  This  gives  an  indication  of  what  may  be  expected 
from  tubes  of  ordinary  dimensions  based  on  these  thermionic  currents. 

A  curious  effect  is  encountered  when  the  joint  filament  heating 
and  thermionic  (pure  electron)  currents  are  combined.  In  the  fila- 
ment heating  circuit  shown  in  Figure  74,  the  current  circulates  in 
the  direction  indicated  by  the  dotted  arrows.  Under  normal  condi- 
tions, therefore,  the  ammeters  A^  and  A2  read  the  same.  If,  however, 


FIGURE  74 — Illustrating  Combined  Lighting 
and  Thermionic  Currents. 


the  plate  circuit  is  closed,  and  a  current  indicated  by  A3  appears  in 
that  circuit,  its  direction  of  flow  will  be  as  indicated  by  the  full  line 
arrows.  (It  is  understood  that  the  direction  of  current  flow  is  opposite 
to  that  of  the  negative  electrons,  in  accordance  with  the  commonly 
accepted  convention).  It  will  be  noticed  that  the  plate  current  A3,  will 
flow  outward  from  both  ends  of  the  filament.  Consequently,  at  the 
lower  end  it  will  assist  the  lighting  current,  while  at  the  upper  end 


'Thermionic  Vacuum" 


81 


it  will  oppose  it.  So  that,  if  A  is  the  true  lighting  current,  the  read- 
ings of  the  ammeters  will  be  given  by  AI=A-}-A3  and  A^=^A — A3. 
With  small  tubes,  such  as  might  be  used  for  receiving,  this  effect  is 
of  no  practical  importance,  but  on  larger,  heavy  plate  current  tubes 
(with  filaments  already  worked  near  the  burn-out  point)  it  may  be- 
come serious. 

This  effect  has  been  ingeniously  minimized  by  Mr.  William  C.  White, 
to  whom  much  of  the  recent  development  of  the  pliotron  is  due,  through 
the  use  of  the  circuit  shown  in  Figure  75.  Here  the  filament  is  lit  by  the 
alternating  current  from  the  secondary  of  the  transformer  T.  The  con- 
nection of  the  plate  circuit  is  made  to  the  middle  of  the  supply  secondary 
winding.  A  similar  method  might  be  applied  to  connection  to  the  middle 


1 


FIGURE  75 — General  Electric  Company- 
White  method  of  plate  circuit 
connection. 

point  of  a  storage  battery  (or  three-wire  direct-current  generator)  used 
for  the  supply  of  lighting  current. 

We  have  assumed  so  far  that  the  vacuum  within  the  bulb  was  prac- 
tically '  *  perfect ' ' ;  that  is,  a  few  ten-millionths  of  a  millimeter  of  mercury 
or  less.  Furthermore,  by  the  use  of  elaborate  exhausting  and  internal 
heating  methods,  it  is  assumed  that  the  electrodes  have  been  thoroughly 
freed  from  any  occluded  gases  so  that  the  tube  will  remain  constant  in 
operation.  (See  Dr.  Langmuir's  paper  appearing  in  the  September.  1915, 
issue  of  the  "Proceedings  of  the  Institute  of  Radio  Engineers.")  Such 
perfection  of  vacuum  is  not  easily  obtained  or  maintained,  and  tubes 
containing  or  evolving  gas  will  show  markedly  different  effects  from 


82  Deterioration  of  Gas  -  Containing  Tubes 

those  described.    In  the  first  place,  the  current  between  plate  and  fila- 
ment will  be  much  increased.    The  reason  for  this  is  the  following : 

The  rapidly  moving  electron  stream  will  ionize  by  impact  the  gas 
molecules ;  that  is,  dissociate  the  atoms  into  negative  electrons  and  positive 
ions.  These  positive  ions  will  recombine  with  the  " electron  cloud"  sur- 
rounding the  cathode,  thus  neutralizing  and  destroying  the  effects  of  the 
space  charge.  In  consequence,  tubes  in  which  gas  (and  consequently 
positive  ions)  are  present  will  pass  greater  currents  at  low  plate  voltages 
than  will  the  extremely  high  vacuum  tubes.  Among  tubes  having  present 
positive  ions  (and  diminished  space  charge  effect)  are  the  original  de 
Forest  audions  and  the  von  Lieben-Reisz  oxid  filament  tubes.  At  first 
sight,  it  might  seem  that  the  presence  of  positive  ions  and  increased  cur- 
rent in  the  plate  circuit  was  an  unmixed  advantage,  and  there  is  no 
doubt  that  it  constitutes  a  convenience  in  ordinary  detector  tubes  in 
that  it  permits  the  use  of  comparatively  low  plate  voltages.  On  the 
other  hand,  it  has  at  least  two  marked  disadvantages. 

The  first  of  these  is  the  fairly  rapid  filament  deterioration  of  such 
tubes  when  any  considerable  plate  current  passes.  The  presence  of 
positive  ions  leads  to  ionic  bombardment  of  the  negatively  charged  fila- 
ment. The  positive  ions  are  comparatively  massive  (in  relation  to  the 
negative  electrons)  ;  and  when  they  strike  the  filament  at  fairly  high 
velocities,  the  surface  is  rapidly  damaged.  This  is  not  at  all  the  case  for 
the  high  vacuum  ''pure  electron  discharge"  tubes,  where  positive  ions 
are  not  present.  Furthermore,  when  used  to  pass  any  considerable 
amount  of  plate  current,  the  gas-containing  tubes  may  become  dangerous 
in  that  the  gaseous  ionization  may  rise  to  the  familiar  "blue  glow"  point. 
At  this  point  continuous  and  progressive  ionization  of  the  gas  occurs 
together  with  greatly  increased  plate  current.  While  they  may  not  be 
much  more  than  an  inconvenience  w^ith  small  tubes,  with  large  tubes  at 
high  plate  voltages  it  may  lead  to  disastrous  currents  and  consequent 
violent  tube  destruction.  For  these  reasons,  very  high  vacua  are  generally 
desirable  in  tubes. 

It  is  a  fact,  though  not  well  known,  that  the  usual  Fleming  valve  or 
rectifier  can  be  used  to  produce  sustained  oscillations  when  shunted  by  a 
circuit  of  large  inductance  and  small  capacity  without  any  third  electrode 
or  control  member.  This  method  is  not  used  in  practice  because  of  the 
high  voltages  required,  the  troublesome  large  resistances  in  the  feeding 
circuit,  and  the  very  rapid  deterioration  of  the  tube  and  its  irregular 
operation. 

For  the  production  of  sustained  radio  frequency  oscillations  from 
vacuum  tubes,  a  third  or  control  member  may  be  employed.  This  may 
be  in  the  form  of  a  perforated  plate  or  a  grid  of  wire  placed  between  the 


Grid  Potential  Control  of  Plate  Current 


83 


plate  and  filament  so  that  the  electron  stream  must  pass  through  the 
meshes  of  the  grid.  The  remarkable  mobility  of  the  electron  stream  per- 
mits of  ready  control  of  the  current  between  plate  and  filament.  Dr. 
Langmuir  has  stated  that  the  current  between  plate  and  filament  with 
the  control  member  inserted  is  given  by  the  equation  : 


»'=14.65(10)-6— 


where  i  is  the  current  in  amperes  in  the  plate  circuit,  I  the  length  of  the 
filament  in  centimeters,  r  the  radius  of  the  surrounding  plate  (of  cylin- 
drical form)  in  centimeters,  e  the  voltage  in  the  plate  circuit,  e'  the  grid 
potential  (relative  to  the  filament),  and  k  a  constant.  The  constant,  k,  is 
dependent  on  the  spacing  of  the  grid  wires,  the  distance  of  the  grid  from 
the  plate  and  filament  and  the  construction  of  the  tube.  Roughly  speak- 
ing, the  finer  the  spacing  of  the  grid 
wires,  the  larger  the  constant  k  and  the 
smaller  the  grid  potential  variations 
which  will  completely  control  the  plate 
current.  The  danger  with  fine  grids  is 
that  small  positive  potentials  will  pro- 
duce excessively  large  plate  currents. 
With  a  coarse  grid,  the  control  voltages 
must  be  larger,  but  the  danger  men- 
tioned above  is  minimized. 

The  control  energy  required  for 
producing  the  requisite  grid  potential 
variations  is  quite  small  and  herein  lies 
the  remarkable  amplifying  (and  oscil- 
lating) power  of  the  device.  Aside 
from  grid  leakage  and  grid  charging 
currents  there  are  no  sources  of  energy 
loss  in  the  grid  circuit  inside  the  bulb. 

A  typical  grid  potential-plate  current  curve  is  given  in  Figure  76. 
It  will  be  seen  that  for  large  negative  grid  potentials  (at  A)  practically  no 
current  flows  in  the  plate  circuit.  From  B  to  C  the  current  through  the 
plate  circuit  varies  practically  linearly  with  the  applied  grid  (negative) 
potential,  and  it  is  in  this  range  that  the  tube  should  be  worked  for  radio 
telephonic  oscillation  or  control.  At  C,  the  plate  characteristic  begins  to 
flatten,  until  at  D  practically  no  further  increase  of  plate  current  can  be 
produced  by  more  positive  grid  potential.  The  flattening  of  the  curve  at 
D  may  be  caused  either  by  temperature  or  space  charge  limitation  of  the 
plate  current  and  determines  the  rating  of  the  tube  at  a  given  plate 
voltage. 


for  pure  electron  amplifiers. 


84 


Electron  Relay  Amplification 


In  Figure  77  is  illustrated  the  mode  of  action  of  the  electron  relay 
as  an  amplifier  of  alternating  current.  The  alternator,  A  (which  may, 
of  course,  be  replaced  by  the  oscillating  circuit  condenser  terminals),  is 
connected  to  the  grid  and  filament  of  the  tube.  The  plate  circuit  is  sup- 
plied by  the  battery  B  which,  we  shall  assume,  readily  permits  the  pas- 
sage through  it  of  alternating  current.  If  this  last  is  not  true,  a  large 
condenser  must  be  shunted  across  the  battery,  thus  by-passing  the  alter- 
nating current  without  interfering  with  the  direct  plate  current.  In 
series  with  B  are  connected  the  direct  current  ammeter  A^  the  alter- 
nating current  ammeter,  A2,  and  the  primary  of  the  transformer,  T.  It 


U 


Y 


FIGURE  77 — Amplification  of  alternating 
current  energy. 


is  assumed  that  A1  does  not  impede  the  flow  of  alternating  current  in 
the  plate  circuit ;  otherwise  it  may  have  a  condenser  placed  in  parallel 
with  it.  The  secondary  terminals,  X,  Y,  of  the  transformer  T  constitute 
the  output  terminals  of  the  amplifier  or  "repeater." 

Under  the  conditions  shown,  the  plate  current  will  remain  at  the 
steady  value  indicated  by  AB  in  Figure  78  so  long  as  the  alternator,  A, 
is  not  running.  The  effect  of  closing  the  alternator  circuit  is  shown  at 
BC  in  Figure  78.  In  the  figure  the  median  value  of  the  portion,  BC,  is 
taken  as  equal  to  that  of  AB;  that  is,  it  is  assumed  that  the  fluctuating 


Electron  Relay  Oscillator 


85 


current  swings  up  and  down  around  an  average  value  equal  to  the  orig- 
inal direct  current.  This  is  generally  not  the  case;  since  grid  circuit 
rectification,  flattening  of  the  grid  potential-plate  current  characteristic, 
or  occasional  positive  grid  charges  may  cause  the  average  plate  current 
to  go  up,  remain  fixed,  or  drop  when  the  alternating  potential  difference 

is  applied  to  the  grid  and  filament.  In 
any  case,  however,  the  pulsations  in 
current  in  the  plate  circuit  will  be 
marked  if  the  grid  potential  variations 
are  sufficient,  and  there  will  be  avail- 
able at  the  terminals,  X,  Y,  the  am- 
plified energy.  As  shown,  the  device 
may  obviously  be  used  as  an  audio  or 
radio  frequency  amplifier,  and  is  in- 
deed so  employed  respectively  in  the 
trans-continental  wire  telephone  lines 
and  in  ordinary  receiving  radio  sets. 
It  has  been  pointed  out  that  the 
energy  delivered  at  the  terminals, 
X,  Y,  is  many  times  greater  than  that 
required  at  the  terminals,  U,  V,  of  the 
alternator.  For  example,  there  may  be  available  at  X,  Y,  10  watts,  while 
only  1  watt  is  required  at  U,  V.  It  would  immediately  seem  that  if  one 
of  the  10  watts  available  at  X,  Y,  were  transferred  back  to  U,  V,  by 


B 


-TlME- 
FIGURE  78 — Plate  current-time  curve. 


FIGURE  79 — Oscillating  circuit. 

coupling  or  otherwise,  the  alternator  might  be  removed,  but  the  system 
would  continue  to  sing  or  oscillate  steadily  as  a  generator  of  alternating 
current.  A  typical  circuit  arrangement,  shown  by  E.  H.  Armstrong,  for 


86 


Plate  Circuit  Tuning  of  Oscillator 


securing  this  so-called  "regenerative  coupling"  is  given  in  Figure  79.* 
It  will  be  seen  that  the  arrangement  is  similar  in  principle  to  Figure  77, 
except  that  the  alternator,  A,  has  been  replaced  by  the  oscillating  circuit, 
L  I!  C,  or  rather  by  the  condenser  terminals  of  C.  In  addition,  there 


FIGURE  80 — Plate  circuit  tuning  in  oscil- 
lating circuit. 


has  been  added  the  coupling,  L'  L",  between  the  grid  circuit,  L  L'  C,  and 
the  plate  circuit,  L"  B.  A  system  such  as  that  shown  will  oscillate  vigor- 
ously if  the  circuit  constants  are  properly  chosen.  The  output  energy  is 
in  general  obtained  by  coupling  to  a  coil  inserted  in  the  plate  circuit.  It 
is  this  type  of  oscillator,  which,  used  as  a  detector  also,  is  so  directly  ap- 
plicable to  long  distance  beat  reception ;  and  has  accordingly  been  widely 
applied  for  that  purpose. 

An  improvement  on  the  simple  circuit  of  Figure  79  has  been  shown 
by  Armstrong,  and  is  given  in  Figure  80.*  It  contains  an  added  in- 
ductance, L",  in  the  plate  circuit  and  a  condenser,  C',  across  the  terminals 
of  L'  and  L"  whereby  the  plate  circuit  may  be  tuned  to  the  same  fre- 
quency as  the  grid  circuit  or  approximately  so.  The  efficiency  and  output 
of  the  oscillator  are  generally  increased  by  such  an  arrangement;  but, 
on  the  other  hand,  the  complexity  of  apparatus  and  difficulty  of  adjust- 
ment may  sometimes  become  undesirable. 

In  working  with  the  various  types  of  oscillating  circuits  to  be  shown, 
it  is  quite  essential  that  the  grid  connection  shall  be  to  such  a  point  of 
the  conjoint  grid  and  plate  circuits  that  the  electromotive  forces  placed 
on  the  grid  are  in  the  proper  phase  relation  to  the  alternating  current 


1915. 


*  "Proceedings  of  the  Institute  of  Radio  Engineers,"  Volume  3,  number  3,  September, 


Meissner  Oscillating  Circuits 


87 


produced  in  the  plate  circuit,  otherwise  the  system  will  not  persist  in 
oscillation. 

A  form  of  oscillating  circuit  of  simple  electrical  nature,  due  to  Dr.  A. 


FIGURE  81 — Meissner  oscillating  circuit,  1913. 

Meissner  of  the  Telefunken  Company,  and  invented  before  March,  1913, 
will  be  next  considered.  The  circuit  is  shown  in  Figure  81.  It  will  be 
seen  that  the  grid  and  plate  circuits  are  coupled,  but  indirectly,  through 


L1 


l!1 


-HBBH 


FIGURE  82 — Arco-Meissner  oscillating 
circuit. 


the  tuned  circuit  L  L'  C.  The  inductance,  L,  of  this  circuit  is  coupled  to 
the  plate  circuit,  while  the  inductance,  L' ',  of  the  same  circuit  is  coupled 
to  the  grid  circuit.  In  consequence,  sustained  alternating  current  will  be 


88 


Lieben-Reisz  Oxide  Filament  Tube 


produced  in  the  circuit,  L  L'  C,  as  previously  indicated.  In  practice, 
resistance  may  be  inserted  in  the  circuit,  L  L'  C,  for  absorbing  the  output 
of  the  system;  and  in  fact,  the  capacity,  C  (and  the  resistance  just  re- 
ferred to),  are  replaced  by  the  antenna  when  radiation  is  desired.  An- 
other form  of  circuit  used  by  the  same  company,  and  the  joint  invention 
of  'Count  Arco  and  Dr.  Meissner  in  1914  is  shown  in  Figure  82.  It 

differs  from  that  previously  shown  in 
that  the  intermediate  coupling  circuit 
is  replaced  by  a  direct  inductive 
coupling  between  grid  and  plate  cir- 
cuits. This  coupling,  L  L',  links  the 
\  grid  circuit  to  the  tuned,  absorbing 

plate  circuit,  L'  L"  C,  which,  as  be- 
fore, may  either  contain  the  antenna 
or  be  coupled  thereto. 

An  interesting  type  of  bulb  was 
used  by  Dr.  Meissner  in  his  experi- 
ments ;  and  a  photograph  of  this  bulb 
is  shown  in  Fig.  83.  Bulbs  of  this 
sort  give  current  amplifications  up  to 
thirty  times.  It  must  be  at  once  men- 
tioned that  these  are  not  high  vacuum 
bulbs,  an  atmosphere  of  mercury 
vapor  being  purposely  provided  by 
the  small  piece  of  mercury  amalgam 
shown  sealed  into  the  small  side  tube 
at  the  bottom  of  the  tube.  The  result 
of  this  vapor  and  the  oxide-coated 
Wehnelt  (heated)  cathode  is  that  the 
tube  in  operation  shows  a  continuous 
blue  glow. 

As  has  been  stated,  the  filament 
is  a  platinum  strip,  about  a  meter 
(3  feet)  long  in  all,  1  mm.  (0.04  inch) 
wide,  and  0.02  mm.  (0.002  inch) 
thick.  It  is  thinly  coated  with  a  mix- 
ture of  calcium  and  barium  oxides, 
and  is  brought  to  a  bright  red  heat 

by  a  current  of  about  2  amperes  from  a  28  to  32  volt  storage  battery,  the 
current  being  regulated  by  a  5  ohm  variable  series  resistance.  Consider- 
able heating  power  is,  therefore,  required ;  and  the  source  of  this  power 
must  be  an  extremely  constant  one. 


FIGURE    83 — Lieben    tube    of 
Telefunken  Company. 


Franklin  Oscillating  Circuit 


89 


The  plate  circuit  is  fed  from  a  220-volt  source  which  may  be  an 
ordinary  dynamo  with  choke  coils  in  the  supply  leads  to  cut  down  the 
incidental  noises.  The  plate  circuit  current  is  about  0.01  ampere,  and 
the  dark  space  interrupting  the  blue  glow  above  the  grid  can  be  used  for 
rough  indication  of  the  current  through  the  plate  circuit.  As  will  be 
seen,  the  plate  itself  is  of  heavy  aluminum  wire. 

The  grid  is  a  perforated  aluminum  sheet,  the  size  of  the  perforations 
being  about  3.5  mm.  (0.14  inch).  It  will  be  noted  that  all  connections  to 
this  bulb  are  made  through  the  bayonet  socket  in  the  base,  this  being  so 
arranged  that  the  bulb  can  be  placed  in  its  socket  only  in  the  correct 
position.  The  life  of  these  tubes  is  claimed  to  be  1,000  hours  or  more. 


FIGURE     84 — Marconi     Company-Franklin 
Circuit,  1914. 

When  used  as  an  oscillator,  wave  lengths  as  short  as  five  or  ten 
meters  Have  been  obtained,  and  with  great  constancy.  Using  a  plate 
voltage  of  440  (instead  of  the  usual  220),  twelve  watts  have  been  trans- 
ferred to  an  antenna,  corresponding  to  an  antenna  current  of  1.3  ampere 
in  a  7-ohm  antenna  at  600  meters  wave-length. 

One  of  the  circuits  devised  in  1914  by  Mr.  Franklin  of  Marconi's 
Wireless  Telegraph  Company  of  England  is  shown  in  Figure  84.*  It  will 
be  noticed  that  the  plate  oscillating  circuit  is  tuned  by  means  of  the  con- 
denser, C",  and  that  one  of  its  inductances,  L",  is  coupled  to  the  grid 
circuit  inductance,  L'.  The  grid  circuit,  L  Lr  C,  is  also  tuned.  Energetic 

*  British  patent.  No.   13,248,  of  1914. 


90 


Marconi  Company  Oscillating  Circuit 


oscillations  can  thus  be  obtained.  It  will  be  noticed  further  that  there 
is  included  in  the  circuit  between  filament  and  grid  the  battery,  Bf.  The 
purpose  of  this  battery  is  to  enable  choosing  such  normal  grid  potential 
as  shall  give  a  desired  plate  current  through  the  bulb,  and  desired  output 
with  high  efficiency.  Indeed,  it  is  necessary  with  most  bulbs  to  keep  the 
grid  at  a  negative  potential,  since,  if  the  grid  becomes  positive,  current 
begins  to  flow  from  the  grid  to  the  filament  with  consequent  absorption 
of  energy  in  the  grid  circuit.  The  amplifying  action  of  the  tube  and  its 
efficiency  as  a  sustained  current  generator  are  then  impaired. 


FIGURE    85 — English     Marconi     Company 
oscillating  circuit;  modified  form. 


In  Figure  85  is  shown  a  simplified  diagram  of  another  form  of  trans- 
mitting circuit  used  by  the  English  Marconi  Company  in  its  ship  radio- 
phone transmitters.  The  details  of  the  wiring  diagram  will  be  given 
under  ' '  Control  Systems. "  It  need  only  be  mentioned  that  the  alternat- 
ing current  energy  is  withdrawn  from  the  oscillator  at  Z/j. 

Dr.  de  Forest  has  carried  on  extensive  experiments  with  vacuum  tube 
oscillators.  One  of  the  earliest  and  simplest  circuits  is  his  ' '  ultraudion ' ' 
circuit,  shown  in  Figure  86.  It  is  normally  used  in  receiving,  though  it 
is  naturally  available  also  for  generation  of  greater  power.  As  shown, 
the  telephone  T  and  battery  B  in  the  plate  circuit  are  shunted  by  a 
"bridging  condenser"  C".  Connected  between  the  plate  and  grid  is  the 


de  Forest  "Ultraudion"  Circuit 


91 


oscillating  circuit,  L  C,  one  side  of  which  is  directly  connected  to  the 
plate,  and  the  other  to  the  grid  by  the  small  condenser,  C".  This  condenser 
is  usually  shunted  by  a  leakage  resistance  (not  shown  in  the  figure) 


FIGURE  86 — de  Forest  ultraudion  circuit 

rhich  prevents  the  accumulation  of  an  excessive  negative  charge  on  the 
grid  and  consequent  limitation  of  the  plate  current. 

Dr.  de  Forest  explains  the  action  as  follows:    "There  is  only  one 
oscillating  circuit.    This  circuit  is  such  that  a  sudden  change  of  potential 


FIGURE  87 — de  Forest  oscillating  circuit, 
1915. 

impressed  on  the  plate  produces  in  turn  a  change  in  the  potential  im- 
pressed on  the  grid  of  such  a  character  as  to  produce,  in  its  turn,  an 
opposite  change  of  value  of  potential  on  the  plate,  etc.  Thus  the  to-and- 


92 


de  Forest  High  Power  Tubes 


fro  action  is  reciprocal  and  self -sustaining. "  In  thus  explaining  the 
action  of  the  device,  Dr.  de  Forest  takes  sharp  issue  with  Mr.  Armstrong, 
who  claims  that  the  circuit  is  "regenerative"  in  the  sense  that  there  is 
an  inductive-capacitive  coupling  between  the  plate  and  grid  circuits, 
which  latter  circuits  are  claimed  by  Mr.  Armstrong  to  be  existent  and 
clearly  denned. 

A  later  oscillating  circuit  (1915),  due  to  de  Forest,  is  shown  in 
Figure  87.  It  will  be  seen  that  this  circuit  differs  from  the  normal 
ultraudion  in  that  there  is  a  coupling  added  between  the  grid  and  plate 
circuits.  This  coupling  is  L'  and  L"  and  is  presumably  intended  to  rein- 
force the  production  of  oscillations  and  produced  greater  outputs  in  con- 
sequence. The  coil,  L" ',  is  referred  to  as  a  "tickler"  coil. 

The  question  of  considerable  outputs 
from  vacuum  tube  oscillators  has  led  to  the 
consideration  of  methods  of  heat-resistant 
tube  construction.  An  attempt  in  this  di- 
rection is  shown  in  Figure  88  and  is  due  to 
de  Forest.  The  two  metal  vessels,  6  and  7, 
are  so  arranged  that  the  space  between  them 
is  filled  by  a  heat-conducting  fluid,  e.  g., 
mercury  or  certain  oils.  This  fluid  acts  at 
the  same  time  as  a  means  of  sealing  the 
inner  vessel  and  of  preventing  air  leakage. 
The  grid,  filament,  and  plate  structure  are 
mounted  inside  the  inner  vessel  in  the  usual 
manner.  The  inner  vessel  is  corrugated  in 
the  region,  20,  so  as  to  provide  plenty  of 
heat  conducting  surface  where  this  is  most 
needed. 

FIGURE    88 — de    Forest    high-  .  _ 

power  tube  construction.  The  General  Electric  Company  has  de- 

veloped a  number  of  types  of  extremely 

high  vacuum  tubes  and  the  circuits  necessary  for  their  use.  One  of  the 
simplest  of  these,  and  one  having  marked  advantages,  is  shown  in  Figure 
89.  Here  both  plate  circuit  L"  C"  G  and  grid  circuit  L'  C'  are  tuned 
and  coupled  to  each  other.  The  output  circuit  is  connected  to  the  in- 
ductance, L,  coupled  as  shown.  A  unique  feature  of  the  circuit  is  that 
the  same  generator,  G,  is  used  both  for  lighting  the  filament  through  the 
auxiliary  regulating  resistance,  E,  and  for  supplying  the  plate  circuit 
directly.  It  is  thus  possible  to  connect  such  an  arrangement  directly  to 
a  single  source  of  direct  current  and 'to  start  the  oscillation  by  merely 
closing  a  single  switch.  Such  automatic  action  is  a  desideratum  in  radio- 
phone equipment. 


General  Electric  Company  Pliotron 


93 


The  actual  appearance  of  the  General  Electric  pliotron  or  three- 
electrode  tube  is  indicated  in  Figures  90,  91,  and  92.  The  first  of  these 
figures  shows  the  mode  of  mounting  the  filament  and  grid  member  of  a 
pliotron.  The  "W"  filament  is  suitably  anchored  and  supported.  The 
grid  itself  is  wound  on  a  tungsten  frame.  Figure  91  represents  a  later 
type  of  filament  and  grid  support.  This  type  has  increased  rigidity  and 
is  more  heat  resistant.  In  addition,  the  insulation  has  been  improved, 
particularly  with  a  view  to  resisting  the  extremely  high  temperatures 
attained  within  the  bulbs  when  in  operation.  The  appearance  of  one  of 
the  complete  bulbs  is  clearly  shown  in  Figure  92.  The  massive  tungsten 


FIGURE     89 — General     Electric     Company 
oscillating  circuit. 


plates  are  seen  to  be  properly  supported  outside  the  filament  grid  struc- 
ture, and  from  the  opposite  end  of  the  tube.  Tubes  of  this  sort  can 
stand  thousands,  and  even  tens  of  thousands,  of  volts  between  plate  and 
filament  without  showing  any  blue  glow  due  to  gas  present  in  the  tube. 
The  output  of  even  a  comparatively  small  tube  of  the  type  shown  in 
Figure  92  runs  into  hundreds  of  watts  at  plate  voltages  of  about  one 
thousand  volts.  Such  tubes  and  the  circuits  associated  with  them  will  be 
further  considered  under  a  later  heading,  wherein  complete  radiophone 
sets  of  the  General  Electric  Company  are  shown. 

"We  consider  next  certain  phases  of  the  work  of  the  Western  Electric 
Company.     A  circuit  used  for  the  production  of  oscillations  by  that 


94 


Western  Electric  Company  Oscillating  Circuit 


company  and  due  to  Mr.  Edwin  Colpitts  in  1915  is  shown  in  Figure  93. 
The  plate  circuit  is  fed  from  the  battery,  B,  which  is  in  series  with  the 
choke  coil  or  inductance,  L^.  Consequently  the  plate  voltage  does  not 
remain  constant.  The  tuned  plate  oscillating  circuit  is  L'  C',  this  being 
inductively  coupled  to  the  tuned  grid  circuit,  L  C.  The  grid  is  main- 
tained at  a  negative  potential  by  means  of  the  battery,  B',  the  oscillations 
impressed  on  the  grid  being  prevented  from  passing  through  the  battery, 
B',  by  means  of  the  inductance,  L2.  The  output  of  the  bulb  is  drawn 
from  the  coil,  L",  which  is  inductively  coupled  to  the  inductance  in  the 
plate  circuit. 


FIGURE  90 — Filament  and 
grid  element  of  pliotron. 


FIGURE  91 — Filament  and 
grid  element  of  pliotron. 


A  line  of  development  which  the  Western  Electric  Company,  among 
others,  has  pursued  in  connection  with  the  obtaining  of  considerable 
outputs  has  been  the  amplification  of  the  output  of  a  single  oscillator  by 
a  bank  or  banks  of  vacuum  tube  amplifiers,  these  individual  amplifiers 
being  placed  in  groups  in  parallel.  While  apparatus  of  this  type  tends 


Heising  Oscillator — Amplifier  System 


95 


FIGURE    92 — General    Electric 
Company  pilot  rou. 


to  become  bulky  and  clumsy  when  a  very 
considerable  number  of  bulbs  are  used,  it 
has  considerable  electrical  flexibility.  An 
arrangement  of  this  sort  due  to  Mr.  R. 
Heising  is  shown  in  Figure  94.  Herein 
the  oscillator  Af  is  coupled  inductively  to 
the  combined  grid  circuit  of  a  number  of 
amplifying  bulbs,  A',  A'.  The  grids  of 
these  bulbs  are  maintained  at  a  suitable 
negative  potential  by  the  battery,  B'. 
The  circuit,  L  C,  is  tuned  to  the  oscillator 
frequency.  The  resistance,  R  (which  is 
non-inductive),  is  shunted  across  C  so 
that  the  sharpness  of  resonance  of  the 
combined  circuit  is  adjustable  and  that 
its  impedance  at  a  definite  frequency 
shall  have  a  sharply  defined  value.  As 
will  be  seen,  all  the  grids  of  the  ampli- 
fiers, A',  are  connected  in  parallel,  as  are 
also  their  plates.  A  common  plate  bat- 
tery, B,  feeds  all  of  them.  In  series 
therewith  is  an  inductance  which  is 
coupled  to  the  circuit,  Lf  R'  C',  this  latter 
being  the  input  circuit  of  the  second  bank 
of  amplifiers,  A",  A".  In  this  way  the 
amplified  voltages  which  are  produced  in 
the  plate  circuit  of  the  first  bank  of  am- 
plifiers are  brought  to  the  grids  of  the 


FIGURE  93 — Western  Electric  Company — Colpitts  oscillating  circuit. 


96 


Western  Electric  Company  High  Power  Tubes 


second  bank  of  amplifiers.  This  second  bank  of  amplifiers  is  intended 
for  increasing  the  alternating  current  in  the  output  circuit,  whereas  the 
first  bank  was  intended  primarily  for  a  voltage  increase.  The  resistance, 
R',  is  inserted  in  the  grid  input  circuit  of  the  second  bank  of  amplifiers 
to  render  the  operation  more  stable.  The  plate  circuit  of  all  the  ampli- 
fiers, A",  are  fed  from  the  common  battery,  B",  and  an  inductance  in  this 
plate  circuit  is  coupled  to  the  antenna  tuning  coil,  L".  By  this  means 


B'  B  B'  B"       j 

FIGURE  94 — Western  Electric  Company-Heising  oscillator — amplifier  arrangement. 


the  amplified  currents  are  set  up  in  the  antenna  or  final  output  circuit. 
This  system  will  be  further  considered  under  another  heading  in  connec- 
tion with  the  radiophone  work  of  the  Western  Electric  Company. 

The  construction  of  vacuum  bulbs  for  large  outputs  has  engaged  the 
attention  of  the  engineers  of  this  company  as  well.  A  well-defined  trend 
of  their  development  has  been  the  attempt  to  secure  very  effective  control 


FIGURE     95 — Western     Electric     Company — Nicolson 
high-power  bulb. 


by  placing  the  filament  and  grid  very  close  together.  In  fact,  actual  con- 
tact (though  with  an  insulator,  such  as  nickelous  oxide,  between)  has 
been  considered.  The  arrangements  developed  for  this  purpose  will  be 
considered  in  greater  detail  in  connection  with  receiving  apparatus.  For 
transmitting  work  Mr.  A.  Nicolson  has  developed  the  type  of  bulb  shown 
in  Figure  95.  A  glass  tube,  A,  of  cylindrical  form,  is  sealed  inside 


General  Electric  Company — Hull  Dynatron 


97 


another  cylindrical  glass  tube,  B,  and  the  space  between  is  exhausted 
through  the  seal  C. 

Prior  to  the  exhaustion,  the  filament,  grid,  and  plate  members  are 
inserted  or  slid  into  the  space  between  the  inner  and  outer  tubes.  The 
filament  is  a  twisted  platinum  strip  coated  with  nickelous  oxide  and 
wound  around  the  metal  cylinder  E,  which  is  the  grid.  The  filament,  Z>, 
is  represented  by  the  two  lines  of  crosses  along  the  length  of  the  cylin- 
drical grid.  The  filament  terminals  are  brought  out  of  the  tube  through 
the  leads,  J  and  G.  It  will  be  noticed  that  the  grid  is  internal  to  the  fila- 
ment in  this  particular  tube,  a  comparatively  rare  construction.  The  grid 
lead  out  of  the  tube  is  K.  The  plate  is  the  outer  cylinder,  F,  and  its 
connection  to  the  outside  of  the  tube  is  H.  The  plate  is  inserted  into  the 
tube  at  the  same  time  as  the  grid  and  filament,  that  is,  before  exhaustion. 


FIGURE  96 — General  Electric  Company— Hull 
dynatron  amplifier  circuit. 


Cooling  of  the  tube  is  accomplished  by  passing  a  liquid  or  gas  through 
the  central  orifice  as  indicated  by  the  arrows,  L.  The  exterior  portions 
of  the  tube  are  similarly  cooled,  and  this  is  claimed  to  enable  the  tube  to 
operate  continuously  with  heavy  plate  currents. 

Through  the  courtesy  of  the  General  Electric  Company  and  Dr. 
Albert  W.  Hull,  we  are  enabled  to  present  to  our  readers  a  more  recent 
development  in  vacuum  tube  amplifiers  and  oscillators,  namely  ' '  the  dyna- 
tron. ' '  This  device  depends  on  a  principle  hitherto  not  used  in  this  con- 
nection, namely  secondary  emission.  This  phenomenon  is  as  follows: 
When  a  stream  of  rapidly  moving  negative  electrons  falls  on  a  metal 
plate,  if  the  velocity  of  the  stream  is  not  very  great,  no  unusual  effect 
will  be  noticed.  If  the  velocity  is  somewhat  increased  each  electron  im- 


98 


Dynatron  Construction 


pinging  on  the  plate  will  liberate  from  the  molecule  which  it  strikes  one 
slowly  moving  electron.  As  the  velocity  of  the  impinging  or  ' '  primary ' ' 
electron  stream  is  increased,  at  each  collision,  two  electrons  will  be  lib- 
erated from  the  plate,  and  the  number  of  ' '  secondary ' '  electrons  liberated 
by  each  primary  electron  on  impact  may  be  as  many  as  twenty  for  very 
high  primary  electron  velocities. 

Let  us  now  consider  the  arrangement  of  circuits  shown  in  Figure  96. 
The  bulb  shown  is  a  dy natron,  containing  an  incandescent  filament,  F, 
an  anode,  A  (which  is  a  perforated  plate),  and  the  plate,  P.  It  is  at  once 
to  be  noted  that  the  anode,  A,  is  not  a  grid,  being  maintained  at  a  fixed 
and  high  positive  potential  and  not  serving  as  an  input  member  of  the 
system.  Unless  this  is  kept  in  mind,  the  action  of  the  device  can  not  be 


VOLTAGE       / 


FIGURE    97 — Dynatron    voltage    amplifier 
characteristics. 


understood.  The  filament  is  maintained  incandescent  by  the  battery,  B. 
Between  the  filament  and  the  anode,  A,  is  connected  the  battery,  B' ',  with 
its  positive  end  connected  to  A.  So  far  the  device  will  act  just  as  does 
an  ordinary  hot  cathode  rectifier,  e.  g.,  a  kenotron,  with  the  exception 
that  a  great  number  of  electrons  moving  from  the  filament,  F,  to  the 
anode,  A,  will  pass  through  the  hole  or  holes  in  the  anode  and  strike  the 
plate.  So  long  as  the  velocity  of  the  electrons  striking  the  plate,  P,  is 
not  high,  the  curve  connecting  applied  voltage  (between  the  plate,  P.  and 
the  filament,  F)  and  the  current  flowing  in  the  plate  circuit  (e.  g.,  be- 
tween points  E  and  F)  will  be  similar  to  that  for  a  kenotron.  Suppose 
for  the  present  the  resistance,  R,  in  the  plate  circuit  to  be  zero.  As  long, 


Dynatron  Negative  Resistance 


99 


then,  as  the  tap,  D,  is  so  placed  that  the  plate  is  not  very  positive,  we  get 
the  usual  characteristic  indicated  by  the  portion  OA  of  the  curve  of 
Figure  97,  which,  as  stated,  resembles  the  normal  current-voltage  curve 
of  a  kenotron  rectifier. 

As  we  approach  the  point,  A,  of  the  curve,  however  (by  raising  the 
voltage  of  the  plate  by  moving  the  tap,  D,  up  the  battery,  B'),  the  elec- 
trons striking  the  plate  begin  to  have  higher  velocities  and  secondary 
emission  occurs.  In  consequence  the  electrons  released  by  the  secondary 
emission  are  produced  in  increasing  quantities.  Since  the  anode  is  more 
positive  than  the  plate,  these  electrons  will  be  attracted  to  the  anode  and 
there  absorbed.  As  for  the  plate,  it  begins  to  lose  by  secondary  emission 
an  appreciable  portion  of  the  current  which  strikes  it  so  that  the  net 
current  in  the  plate  circuit  (DFERP)  becomes  smaller  and  smaller  as 
the  plate  voltage  is  increased.  This  is  shown  in  the  portion,  AB,  of  the 
curve  of  Figure  97,  which  shows  that  the  current  in  the  plate  circuit  is 
diminishing  for  increasing  plate  voltage.  At  B  the  plate  loses  as  many 
electrons  as  strike  it,  and  the  net  current  is  zero.  From  B  to  C,  as  the 

voltage  of  the  plate  is  further  in- 
creased, each  electron  that  strikes 
the  plate  liberates  more  than  one 
electron  so  that  the  plate  on  the 
whole  loses  electrons  and  the  plate 
current  is  actually  reversed  and 
negative.  At  C  the  limit  of  re- 

gi    .  .  emission  is  reached,  and  thereafter 

•  rlfir  •*•  the  plate  current  rises  along  the 

curve,  CDE,  as  the  voltage  is  in- 
creased. We  have,  in  the  range, 
ABC,  of  the  applied  plate  voltage 
a  most  curious  effect,  namely  that 


B 


FIGURE  98 — Dynatron  oscillator. 


an  increase  of  voltage  causes  an  in- 
crease of  current  m  the  wrong 
direction.  That  is,  between  volt- 
ages A0  and  00  the  plate-to-filament  circuit  of  the  dynatron  acts  as  a 
true  "negative  resistance"  which,  so  far  from  opposing  the  flow  of 
current,  actually  assists  it.  It  acts,  therefore,  in  a  manner  very  roughly 
analogous  to  the  electrical  (though  not  to  the  physical)  behavior  of  the 
Poulsen  arc  and  is  capable  of  being  an  amplifier  or  oscillator.  The  arc, 
however,  has  a  negative  resistance  characteristic  only  for  increasing 
current,  but  acts  as  an  open  circuit  for  decreasing  current.  The  dyna- 
tron has  a  stable  negative  resistance  in  either  case.  Furthermore,  the 
dynatron  has  no  hysteresis  or  lag,  but  responds  instantaneously,  because 
it  does  not  depend  on  gas  ionization,  as  does  the  arc. 


100 


Dynatron  Amplifier  and  Oscillator 


To  make  the  device  a  strong  amplifier,  we  insert  a  resistance,  E  (in 
Figure  96),  in  the  plate  circuit,  which  resistance  has  a  positive  value 
nearly  equal  to  the  negative  resistance  of  the  dynatron  plate  circuit. 
The  current-voltage  curve  of  such  a  resistance  will  be  parallel  to  the 
line  FG  in  Figure  97,  where  FG  slopes  to  the  right  nearly  as  much  as  AC 
to  the  left.  The  plate  circuit  characteristic  of  the  dynatron  will  then 
become  the  curve  OB'B"E,  which  is  dotted  in  the  figure.  It  will  be 
seen  that  a  very  small  change  of  voltage  in  the  neighborhood  of  the  value, 
B,  will  cause  a  very  great  change  in  the  current  in  the  circuit  from 
B'  to  B".  The  small  exciting  voltage  would  be  inserted  into  the  plate 
circuit,  for  example  between  the  points  E  and  F. 


FIGURE    99 — General    Electric    Company- 
Hull  pliodynatron  controlled  oscillator. 

Since  the  dynatron  is  a  negative  resistance,  it  is  essentially  an  un- 
stable device  and  will,  if  an  oscillating  circuit  is  included  in  the  plate 
circuit,  produce  in  that  oscillating  circuit  sustained  alternating  currents. 
The  circuit  diagram  therefor  is  shown  in  Figure  98,  which  is  quite 
similar  to  Figure  96,  except  that  the  oscillating  circuit,  LC,  is  added  in 
the  plate  circuit.  The  directions  of  current  while  the  capacity,  0,  is 
discharging  are  shown  by  the  small  arrows,  and  it  will  be  seen  that  the 
capacity  discharges  partly  through  the  inductance,  L,  and  partly 
through  the  plate  circuit  of  the  bulb. 

Using  the  dynatron  as  an  amplifier,  voltage  amplifications  of  as 
much  as  1,000-fold  have  been  obtained,  and  100-fold  amplifications  are 
very  readily  available.  Used  as  an  oscillator,  the  dynatron  has  shown 
itself  capable  so  far  of  producing  all  frequencies  between  less  than  one 
cycle  per  second  and  20,000,000  cycles  per  second  (corresponding  to  a 
wave-length  of  15  meters).  The  output  of  a  single  bulb  has  been  as 
much  as  100  watts. 


Dynatron  Structure ;  Pftddyhatron  Circuit  101 


FIGURE  100 — General  Electric  Company-Hull  dynatron, 
showing  internal  structure. 


FIGURE  101 — General  Electric  Company-Hull  pliodynatron  controlled 

oscillator. 


102  Piiodynstron  Construction 

A  still  more  recent  device,  also  due  to  Dr.  Hull,  is  the  pliodynatron, 
a  combination  of  the  pliotron  and  the  dynatron.  This  device  has  a  true 
grid  as  well  as  the  anode  and  plate  electrodes  and  is  an  interesting  four- 
electrode  device.  The  grid,  as  usual,  is  an  electrostatic  control  member, 
and,  if  the  conditions  are  properly  chosen,  enables  the  stable  control  of 
the  oscillating  energy  in  the  circuit,  LC.  That  is,  the  variation  of  the 
grid  potential  (as  determined  by  the  battery,  B",  or  otherwise)  will 
cause  variations  in  the  oscillation  output  of  the  bulb.  This  feature  will 
be  further  considered  under  "Modulation  Control  for  Radio  Telephony," 
page  175.  The  wiring  of  a  pliodynatron  is  clearly  indicated  in  Figure  99. 

The  actual  appearance  of  the  dynatron  is  illustrated  in  Figure  100 
and  of  the  pliodynatron  in  Figure  101.  It  will  be  noted  that  the  anodes 
are  naturally  much  heavier  than  the  grids  of  pliotrons.  which  must,  of 
course,  be  the  case,  since  their  functions  are  quite  different  and  since  they 
must  carry  very  considerable  currents  in  their  own  circuits  and  be  sub- 
jected to  energetic  electron  bombardment. 


CHAPTER  V. 

(d)  ALTERNATORS  OF  RADIO  FREQUENCY;  PROBLEM  OF  CON- 
STRUCTION ;  TYPES  OF  SOLUTION  ;  GOLDSCHMIDT  ALTERNATOR  ; 
FREQUENCY  MULTIPLICATION  BY  "INTERNAL  REFLECTION"; 
CONSTRUCTIONAL  DETAILS;  PRINCIPLE  OF  FERROMAGNETIC 
FREQUENCY  MULTIPLIER;  TELEFUNKEN  COMPANY  FRE- 
QUENCY DOUBLERS  AND  TRIPLERS ;  ARCO  ALTERNATOR  OF 

TELEFUNKEN  COMPANY  ;  ALEXANDERSON  ALTERNATOR  ;  CON- 
STRUCTIONAL DETAILS;  ELECTRICAL  CHARACTERISTICS;  EX- 
PERIMENTS OF  FESSENDEN  AND  NATIONAL  ELECTRIC  SIGNAL- 
ING COMPANY;  EXPERIMENTS  OF  GENERAL  ELECTRIC  COM- 
PANY; ALEXANDERSON  TRIPLE  FREQUENCY  ALTERNATOR. 

(d)  ALTERNATORS  OF  RADIO  FREQUENCY. 

As  we  have  repeatedly  seen,  the  first  necessity  in  radio  telephony 
is  a  steady  stream  of  alternating  current  of  radio  frequency,  available 
for  modulation  into  speech  form.  We  have  treated  in  succession  the  arc, 
radio  frequent  spark,  and  vacuum  tube  generators  of  such  currents  (or 
first  approximations  to  such  currents).  It  would  seem,  at  first  sight, 
as  if  we  had  neglected  deliberately  an  apparently  far  more  natural  and 
simple  means  of  securing  such  currents  and  one  well  known  to  ordinary 
commercial  electrical  engineering.  We  refer,  of  course,  to  the  normal 
alternator. 

As  a  matter  of  fact,  we  have  deferred  the  study  of  the  radio  frequency 
alternator  because  of  the  real  difficulties  in  the  direct  generation  of  such 
very  high  frequency  alternating  currents.  This  will  be  seen  if  we 
consider  the  pitch  or  distance  between  adjacent  armature  windings  for 
a  100,000-cycle  alternator.  If  we  assume  the  diameter  of  the  rotor  to  be 
2.0  feet  (60  cm.)  and  a  normal  speed  of  rotation  of  2,500  revolutions 
per  minute,  we  find  that  the  pole  pitch  has  the  extraordinarily  small 
value  of  0.016  inch  (0.04  cm.),  which  is  entirely  impracticable  when  one 
considers  that  wire  and  insulation  must  all  be  crowded  into  the  winding 
slot.  In  addition,  there  would  have  to  be  4,800  poles. 

It  becomes  necessary,  then,  if  we  persist  in  the  process  of  direct 
generation  of  the  current,  to  have  a  higher  speed  of  rotation,  since  the  pole 


103 


104 


Radio  Frequency  Alternator  Problem 


number  must  obviously  be  reduced.  Suppose  we  choose  the  extremely 
high  speed  of  rotation  of  20,000  revolutions  per  minute.  We  shall  need 
then  600  poles,  and  the  width  of  winding  becomes  0.12  inch  (0.30  cm.) 
approximately.  So  close  a  winding  can  be  accomplished  if  great  care  is 
exercised  in  the  choice  of  wire  insulation  and  in  the  milling  out  of  the 
slots.  The  requirement  of  a  speed  of  rotation  of  20,000  revolutions  per 
second  makes  a  solid  steel  rotor  and  an  alternator  of  the  inductor  type 
essential ;  and  this  is  indeed  the  case  for  the  radio  frequency  alternators 
of  the  present,  which  (with  the  exception  of  the  Goldschmidt  type,  which 
must  have  a  wound  armature  for  electrical  reasons)  are  all  of  the  in- 
ductor type. 

We  shall  see  that  there  are  thus  at  least  three  general  lines  of  en- 
deavor in  connection  with  the  generation  of  radio  frequent  currents  by 
alternators.  These  are,  firstly,  the  multiplication  of  frequency  within 
the  machine  (Goldschmidt  type)  ;  secondly,  the  multiplication  of  fre- 
quency outside  the  machine  (e.  g.,  Arco  alternator  of  the  Telefunken 
Company,  with  frequency  changers),  and,  thirdly,  the  direct  generation 
in  the  machine  of  the  frequency  used  (Alexanderson  alternator  of  the 
General  Electric  Company).  It  is  interesting  to  note  that  a  solution  of 
the  problem  of  producing  currents  of  frequencies  of  the  order  of  50,000 
cycles  per  second  (and  wave-lengths  of  6,000  meters)  turns  out  to  be 


\ 


FIGURE  102 — To-and-fro  motion  on  rotating  platform 
with  equal  periods  of  oscillation  and  rotation. 

possible  for  considerable  output  powers  (100  kilowatts  or  more)  by  all 
three  methods.    The  details  of  these  methods  will  be  next  considered. 

Prior  to  the  consideration  in  detail  of  the  Goldschmidt  radio  fre- 
quency alternator  and  internal  frequency  changer,  we  desire  to  establish 
a  principle  of  interest  in  connection  therewith.  This  principle  can  be 
rendered  clear  from  a  simple  analogy.  Imagine  a  circular  platform  of 
moderate  dimensions  rotating  once  per  minute,  somewhat  in  the  fashion 
of  the  carousels  used  in  amusement  resorts.  Suppose,  further,  that  the 
attendant  elects  to  walk  back  and  forth  along  a  diameter  of  the  rotating 
platform  while  it  is  in  motion,  and  that  he  makes,  one  to-and-fro  trip  in 
one  minute,  that  is,  in  the  same  length  of  time  as  that  required  for  one 


Analogue  of  Goldschmidt  Alternator 


105 


complete  rotation  of  the  platform.  It  is  required  to  find  his  path  as 
viewed  from  an  external  stationary  point,  or,  otherwise  stated,  with 
reference  to  the  fixed  ground  under  the  platform. 

Figure  102  shows  a  series  of  successive  positions  of  the  diametral 
line  along  which  he  walks,  each  position  being  45  degrees  further  ad- 
vanced than  the  preceding  (that  is,  one-eighth  revolution).  The  dotted 
line  with  the  reference  dotted  arrow  at  one  end  indicates  this  diameter 
which,  as  will  be  seen,  has  reversed  its  direction  in  the  half-revolution 
between  positions  1  and  5.  The  position  of  the  man  on  the  diametral 
line  is  indicated  in  each  case  by  the  cross.  It  will  be  seen  that  the  man 
never  succeeds  in  getting  to  the  left  of  the  center  of  the  platform  be- 
cause, as  position  3  is  passed,  he  comes  to  the  reversed  end  of  the  diametral 
line,  that  is,  the  end  away  from  the  arrow. 


j-  -mw 


B 


S fa  for 


Slip  P/fTg. 


FIGURE    103 — Winding    of   Goldschmidt   alternator. 

The  important  point  is  that  the  path  of  the  man  relative  to  the 
ground  (that  is,  the  curve  ABODE)  is  a  closed  curve,  and  that  he  has 
returned  to  his  original  position  in  a  half -revolution  of  the  platform.  In 
other  words,  relative  to  the  ground,  he  moves  in  a  closed  curve  at  twice 
the  speed  or  double  the  frequency  that  the  platform  rotates. 

"We  establish  then  the  principle  that  an  oscillatory  movement  of  fre- 
quency n  taking  place  on  a  system  rotating  with  frequency  n  is  equiva- 


106  Goldschmidt  Alternator  Circuits 

lent  relative  to  fixed  external  points  to  an  oscillation  of  half  the  ampli- 
tude or  width  of  swing  and  of  double  frequency.  The  mathematical 
proof  of  this  principle  for  simple  harmonic  (sinusoidal)  vibrations  is  of 
the  utmost  simplicity,  but  need  not  here  be  given. 

The  diagrammatic  wiring  plan  of  the  Goldschmidt  alternator  is  given 
in  Figure  103.  The  following  description  is  based  on  an  earlier  explana- 
tion of  this  device  by  the  Author.  In  the  figure,  the  battery,  B,  supplies 
the  direct  current  whereby  the  stator  winding,  S,  becomes  the  field  mag- 
net of  the  alternator.  L  is  a  large  inductance  intended  to  prevent  the 
now  of  alternating  currents  through  the  battery  circuit.  In  the  field  of 
the  stator,  S,  is  a  rotor,  R,  which  is  short-circuited  (that  is,  tuned  to 
resonance)  for  the  fundamental  frequency  produced  when  the  rotor  is 
revolved.  The  tuning  of  the  rotor  circuit  is  accomplished  by  means  of 
the  capacities,  C3  and  C4,  and  the  inductance,  L2.  It  is  to  be  noted  that 
R  and  C3  alone  would  be  in  resonance  to  the  fundamental  frequency,  as 
also  would  L2  and  C4.  The  complete  circuit,  R  C3  L2  C4,  therefore  con- 
tains approximately  twice  the  inductance  and  half  the  capacity  of  either 
R  C3  or  L2  (74.  Its  period,  therefore,  is  the  same  as  that  of  either  of 
these,  and  even  if  L2  C4  were  to  be  short-circuited,  the  rotor  would  still 
be  resonant  to  the  fundamental  frequency.  This  permits  shunting  the 
condenser,  C5,  across  the  circuit,  L»  C4,  without  disturbing  the  tuning. 
A  perfectly  similar  arrangement  is  adopted  for  the  stator  by  the  use  of 
the  circuit,  S  C1  L^  C2t  except  that  the  circuit  in  question  is  tuned  to 
twice  the  fundamental  frequency.  It  will  be  seen  that  as  the  rotor  re- 
volves in  the  field  of  the  stator,  powerful  currents  of  the  fundamental 
frequency  will  flow  through  it.  The  great  magnitude  of  these  currents 
is  due  to  the  fact  that  the  rotor  is  itself  part  of  a  circuit  resonant  to  the 
fundamental  frequency.  If  we  consider  the  field  of  the  rotor,  we  see 
that  it  is  a  field  produced  by  an  alternating  current  of  fundamental  fre- 
quency n  itself  rotating  with  a  frequency,  n.  Therefore,  by  the  principle 
established  at  the  beginning  of  this  discussion,  we  may  regard  it  as  con- 
taining a  component  field  of  constant  magnitude,  but  rotating  with  a 
doubled  frequency,  2n,  relative  to  the  stator.  A  further  study  of  the 
phenomena  would  show  that  there  was  also  present  a  constant  field  ro- 
tating with  velocity  0.  The  rotor  fields  will  therefore  induce  in  the 
stator  electromotive  forces  of  twice  the  fundamental  frequency  (and  zero 
frequency)  ;  and  since  a  circuit  resonant  to  the  double  frequency  is  pro- 
vided, powerful  currents  of  that  frequency  will  flow  through  the  stator. 
These  alternating  currents  in  the  stator  will  induce  in  the  rotor  electro- 
motive forces  of  frequencies,  %  (from  the  steady  field)  and  3n  (from 
the  field  of  the  current  of  frequency  2n) .  By  means  of  the  condenser, 
C5?  a  path  resonant  to  the  frequency,  3n  is  provided  in  the  rotor.  By 


Goldschmidt  Alternator  Construction 


107 


properly  choosing  the  constants  of  the  rotor  circuits,  the  current  of  fre- 
quency n  just  mentioned  can  be  made  nearly  to  neutralise  the  current 
of  frequency  n  first  mentioned.  The  reason  for  this  is  that  these  currents 
can  be  brought  to  nearly  complete  opposition  in  phase  and  equal  ampli- 
tude. There  will  be  left  then  in  the  rotor  a  powerful  current  of  triple 
frequency.  Its  field  may  be  regarded,  by  a  process  of  reasoning  quite 
similar  to  that  originally  employed,  as  equivalent  to  two  constant  and 
equal  rotating  fields,  revolving  in  opposite  directions,  with  speeds  of  ro- 
tation corresponding  to  2n  and  4w.  There  will,  therefore,  be  induced  in 
the  stator  currents  of  frequency  2n  and  4n.  Of  these,  the  current  of 
frequency  2n  will  nearly  completely  neutralise  the  current  of  frequency 
2n  mentioned  previously  if  the  stator  constants  are  properly  chosen. 
The  outstanding  current  of  frequency  4n  is  shown  in  the  figure  as  flow- 
ing into  the  capacity  and  inductance  formed  by  the  antenna,  A,  and  the 
ground,  B.  We  have,  therefore,  by  " internal  reflection"  of  energy, 
quadrupled  the  original  frequency  of  the  machine  before  using  it  for 
antenna  excitation. 

In  the  actual  Goldschmidt  installations  (at  Tuckerton,  New  Jersey, 
and  Eilvese,  Germany,)  the  motor  drive  of  the  alternator  is  accomplished 
by  a  220-volt,  direct  current,  250-horse  power  motor  having  a  speed  of 
4,000  R.  P.  M.  For  constant  speed,  a  special  form  of  sending  key  is  used. 
This  is  shown  in  Figure  104.  This  key  automatically  inserts  (by  opening 


p 

— mm 


Exc/Jer 


Motor 
Field 


iMWBMr 

Sfafor 


FIGURE  104 — Goldschmidt  alternator  speed  constancy  system. 

the  back  stop  circuit)  the  resistance,  R',  in  the  motor  field  circuit  just 
before  the  load  is  thrown  on  by  closing  the  exciter  circuit  of  the  alter- 
nator (by  the  front  contact  of  the  key).  In  this  way  the  motor  tends  to 
speed  up  just  as  load  is  thrown  on,  and  the  speed  actually  remains  con- 
stant. In  addition,  the  inertia  of  the  heavy  armature  helps  greatly. 

The  alternator  itself  is  a  360-pole  machine  having  a  pole  pitch  or 
distance  between  windings  of  7.5  mm.  (0.3  inch),  the  slots  in  which  the 
insulation  and  wire  are  placed  being  circular  and  of  cross  sectional 


108  Goldschmidt  Alternator  Construction 

diameter  of  5  mm.  (0.2  inch).  The  rotor  diameter  is,  therefore,  about 
90  cm.  (3  feet)  and  the  rotor  weighs  about  5  tons  (4,500  kg.).  The 
direct  current  power  required  for  field  excitation  is  about  5  per  cent,  the 
rated  output  of  the  machine. 


D 

FIGURE   105 — Portion  *  of   rotor   or    stator 

winding  of  Goldschrnidt  alternator 

(developed). 

The  winding  of  the  machine  is  one  conductor  per  pole,  being  a 
simple  wave  winding  indicated  in  Figure  105.  AB  and  CD  are  typical 
separate  sections  of  the  winding  so  arranged  that  they  may  be  connected 
in  series  or  parallel,  depending  on  .the  electrical  requirements.  There 
are  twenty-four  such  sections  on  the  total  circumference.  Both  rotor  and 
stator  are  wound  in  the  same  way.  The  wire  itself  is  very  finely  stranded, 
and  made  of  number  40  Brown  and  Sharpe  gauge*  individual  enamelled 
wires  suitably  twisted.  The  iron  in  the  machine  is  very  finely  laminated, 
the  sheets  being  only  0.05  mm.  (0.002  inch)  thick,  insulated  by  paper 
between,  0.03  mm.  (0.001  inch)  thick.  The  rotor  is  more  than  one-third 
paper,  which  is  a  most  unusual  proportion.  Such  construction  is  par- 
ticularly noteworthy  in  view  of  the  high  speed  of  peripheral  rotation, 
namely  200  meters  (600  feet)  per  second.  The  design  of  the  brushes, 
bearing  on  the  rotor  slip  rings,  and  the  connection  to  these  brushes  re- 
quired careful  consideration,  especially  in  view  of  the  danger  of  burning 
the  slip  rings  of  any  brush  that  was  connected  to  an  output  circuit  of 
greater  or  less  impedance  than  any  of  the  remaining  circuits.  In  this 
connection,  it  must  be  mentioned  that  there  were  really  more  than  one 
pair  of  slip  ring  connections  to  the  rotor  since  a  number  of  the  rotor 
sections  were  placed  in  parallel  outside  the  machine. 

Some  difficulty  was  experienced  in  preventing  the  currents  which 
were  generated  from  escaping  to  ground  through  the  capacity  (in  air) 
between  the  conducting  wires  and  the  ground.  In  addition,  there  was 
always  the  danger  that  this  air  capacity  would,  in  conjunction  with  the 
inductance  of  one  or  more  of  the  machine  windings,  produce  a  circuit 
resonant  to  one  of  the  frequencies  generated,  whereupon  dangerously 
high  voltages  and  currents  would  have  arisen,  and  the  output  have  disap- 
peared. 

*Diameter  of  number  40  wire  =  0.0031  inch  =  0.079  mm. 


Goldschmidt  Alternators  at  Eilvese 


109 


The  accuracy  of  construction  of  such  machines  is  extreme.  Since  the 
air  gap  clearance  between  rotor  and  stator  is  0.8  mm.  (about  0.03  inch), 
very  accurate  centering  of  the  rotor  was  necessary.  In  addition,  very 
strict  parallelism  of  the  armature  and  stator  slots  was  required,  a  devia- 
tion from  parallelism  of  one  part  in  a  thousand  causing  a  fifth  of  the 
output  of  the  machine  to  disappear ! 

One  of  the  Goldschmidt  alternators  in  use  at  Eilvese  (Hanover, 
Germany),  is  shown  in  Figure  106.  The  machine  is  to  the  right,  the 


FIGURE  106 — Goldschmidt  alternator,  motor,  and  reflection  circuits  at 
Eilvese,  Germany. 

driving  motor  to  the  left.  The  large  brush  surface  chosen  for  the  high- 
speed driving  motor  is  significant.  The  condenser  banks  for  tuning  the 
various  rotor  and  stator  circuits  are  mounted  on  the  walls,  and  are 
typical  mica  condensers.  Some  idea  of  the  difficulty  of  leading  the  radio 
frequency  currents  into  and  out  of  the  machine  may  be  gained  from  the 
leads  which  are  visible.  The  ingenious  fashion  in  which  the  difficulties 
have  been  overcome  is  worthy  of  comment. 

By  January,  1917,  two  such  alternators  were  being  used  in  parallel 
when  necessary,  and  put  275  amperes  into  the  Eilvese  antenna.  Rapid 
telegraphy  at  a  rate  of  200  letters  per  minute  has  been  accomplished 
by  their  use. 


110 


Properties  of  Iron  for  Frequency  Changers 


As  has  been  previously  stated,  the  second  method  of  securing  con- 
siderable amounts  of  sustained  energy  at  radio  frequencies  when  using 
alternators  is  that  wherein  an  alternator  of  moderately  high  frequency  is 
employed  and  the  frequency  is  multiplied  by  external  frequency  changers 
and  not,  as  in  the  Goldschmidt  machine,  by  reflection  of  the  energy  in 
the  machine  itself.  Most  of  the  external  frequency  changers  employed 
at  the  present  time,  particularly  for  considerable  energy,  are  based  on 
the  properties  of  iron.  Before  explaining  them  in  detail,  it  is  desirable 
to  quote  from  a  paper  by  the  Author  on  the  subject  of  ' '  Radio  Frequency 
Changers. ' ' 


H 

FIGURE    107 — Magnetising   force   and   magnetic 
induction  curve  for  iron. 

In  Figure  107  is  shown  a  typical  "B-H"  curve  for  iron.  This  is  the 
curve  which  shows  the  connection  between  the  magnetising  force  (e.  g., 
expressed  in  ampere-turns  or  product  of  current  flowing  through  the 
magnetising  winding  by  the  number  of  turns  of  winding)  and  resulting 
magnetisation  or  magnetic  flux  through  the  iron  core  (referred  to  as  the 
"induction").  "Let  us  suppose  that  the  magnetisation  of  the  iron  has 
been  brought  to  the  point,  x.  If  now,  by  means  of  a  superposed  alter- 
nating magnetising  force  (such  as  may  be  produced  by  having  around 
the  iron  core  an  auxiliary  winding  through  which  flows  alternating  cur- 
rent), equal  increments  and  decrements  be  added  to  the  magnetising 
force,  the  magnetic  induction  will  increase  during  the  positive  half  of  the 
cycle  by  the  small  amount,  ef.  On  the  other  hand,  during  the  negative 
half  of  the  cycle  the  induction  will  diminish  by  the  considerably  larger 
amount,  xd.  The  explanation  of  this  phenomenon  is  found  in  the  well- 
known  magnetic  saturation  qualities  of  iron,  whence  it  results  that  for 
high  magnetising  forces  the  iron  becomes  saturated  and  the  bend  or 


Polarised  Core  Ferromagnetic  Frequency  Changers  111 

"knee"  of  the  curve  which  is  shown  at  x  results.  It  will  be  seen,  then, 
that  though  a  sine-wave  alternating  current  may  be  flowing  through  the 
auxiliary  winding,  the  variation  in  the  magnetic  flux  through  the  iron 
core  will  not  be  sinusoidal  but  distorted,  the  upper  halves  of  the  curve 
being  flattened.  Such  a  deformation  of  the  flux  variation  always  occurs 
when  nearly  saturated  iron  cores  are  used  under  the  conditions  men- 
tioned. However,  such  a  deformation  of  a  sine  curve  always  leads  to  the 
production  of  upper  harmonics  (i.  e.,  high  frequencies  in  a  secondary 
circuit  wound  around  the  same  iron  core),  and  it  is  upon  this  principle 
that  the  entire  series  of  frequency  changers  employing  iron  is  based. ' ' 

An  application  of  the  principle  just  stated  was  shown  by  Epstein 
in  1902  (German  patent  149,761)  and  has  since  been  worked  out  and 
amplified  in  detail  by  Joly  in  1910  and  Vallauri  in  1911.  It  is  now  ex- 
tensively employed  in  various  forms  by  the  Telefunken  Company  under 
the  patents  of  Count  von  Arco  and  Dr.  A.  Meissner.  The  circuit  ar- 
rangement in  a  simple  form  is  shown  in  Figure  108.  As  will  be  seen,  an 


FIGURE  108 — Telefunken  Company  frequency  doubler. 

alternating  current  source,  A,  sends  its  current  through  the  primaries, 
P1  and  Po,  of  each  of  two  transformers  having  iron  cores.  These  pri- 
maries may  be  connected  in  series  or  in  parallel  according  to  the  second- 
ary voltage  and  primary  current  which  may  be  desired.  They  are  wound 
oppositely  relative  to  each  other.  A  direct  current  source,  B,  e.  g.,  a 
storage  battery  or  small  direct  current  generator,  supplies  the  two  aux- 
iliary coils,  Ml  and  M2,  which  coils  are  also  wound  on  the  same  trans- 
former cores.  The  direct  current  coils  are  wound  oppositely.  The  sec- 


112 


Ferromagnetic  Frequency  Changers 


ondaries  of  the  two  transformers,  $x  and  S,2,  are  wound  in  the  same 
direction,  and  connected  as  indicated  in  the  figure. 

The  operation  of  the  device  is  in  the  main  as  follows:  The  direct 
current  flowing  through  M t  and  M2  is  so  chosen  that  the  iron  is  brought 
to  the  knee  of  the  magnetisation  curve,  i.  e.,  the  point,  x,  in  Figure  107. 
In  consequence,  during  half  the  alternating  current  cycle,  each  of  the 
transformers  has  a  flattened  addition  to  its  iron  magnetisation  due  to  the 
iron  saturation,  while  during  the  other  half  of  the  cycle  it  has  a  peaked 
diminution  in  its  iron  magnetisation  due  to  the  rapid  drop  of  the  iron 
curve  below  the  point,  x. 

This  effect  is  shown  graphically  in  Figure  109.    In  curve  a  of  the 


a 


Time. 


FIGURE    109 — Iron   magnetisation   curves    for   fre- 
quency doublers. 

figure,  the  fine  horizontal  line  represents  the  constant  magnetisation  pro- 
duced by  the  direct  current  which  flows  continuously.  The  curved  line 
shows  the  actual  magnetisation  which  results  when  the  alternating  cur- 
rent also  flows  in  the  winding,  Plm  It  will  be  seen  that  during  the  positive 
half  of  the  alternating  current  cycle,  there  is  only  a  small  increase  in  the 
iron  magnetisation,  whereas  during  the  negative  half  cycle,  there  is  a 
large  diminution  in  the  iron  magnetisation.  It  will  further  be  noticed 
that  the  direct  current  coils  and  the  alternating  current  coils  on  the  two 
transformers  are  wound  so  that  during  the  positive  half  cycle  they  assist 
each  other  on  one  transformer  and  that  they  simultaneously  oppose  each 
other  on  the  other  transformer.  From  this  it  follows  that  the  induction 
in  the  second  transformer  is  given  by  curve  &,  which  lags  practically  a 
half  cycle  behind  curve  a.  The  resulting  total  magnetisation  is  given  by 
curve  c  and  is  seen  to  contain  a  double  frequency.  Oscillograms  of  the 
voltages  induced  at  the  secondary  terminals  of  each  of  the  transformers 
are  represented  in  Figure  110.  The  voltage  at  the  terminal  of  one  of 


Secondary  Voltage  in  Frequency  Changers 


113 


E,-Ez 


FIGURE  110 — Induced  voltages  in  second- 

arys  of  Telefunken  Company 

frequency   doubler. 


the  transformers  is  given  by  the  curve  Et;  that  at  the  terminals  of  the 
secondary  of  the  other  transformer  by  E^,  and  there  is  also  shown  the 
resultant  voltage,  namely  E^-E2.  The  voltage  curves  are  easily  explicable 
on  the  ground  that  the  voltage  magnitude  is  proportional  to  the  rate  of 
change  of  the  primary  current  so  that  it  is  only  at  times  when  the 


FIGURE  111 — Frequency  doublers  used  in  actual  practice. 


114 


Frequency  Triplers 


primary  .current  is  changing  from  the  flat  portion  to  the  peaked  portion 
that  the  large  secondary  voltages  are  induced.  The  resultant  voltage  is 
seen  to  be  of  * '  double  frequency. ' '  Its  purity  of  wave  is  exaggerated  in 
the  figure. 

Of  course,  the  phenomena  shown  are  for  the  frequency  doubler  with 
no  load  on  the  secondary,  and  these  are  to  some  degree  modified  when 
the  double  frequency  energy  is  withdrawn.  However,  by  secondary 
tuning  and  appropriate  design,  the  same  results  as  outlined  can  be  ob- 
tained. A  more  detailed  diagram,  showing  something  of  the  actual  prac- 
tice with  the  frequency  doublers,  is  given  in  Figure  111.  It  will  be  noted 
that  the  primary  circuit  of  the  alternator  A  is  tuned  by  the  inductances 
LU  Plf  and  P2  and  by  the  condensers  C1  and  CL  It  will  also  be  seen  that 
there  is  a  choke  coil  L2  inserted  in  the  direct  current  magnetising  circuit 
of  the  frequency  changers  to  prevent  injuriously  large  radio  frequency 
currents  from  being  induced  in  this  circuit. 

It  can  further  be  shown,  both  theoretically  and  practically,  that  if 
the  secondaries  of  the  frequency  changer,  8±  and  $2  are  connected  assist- 


FIGURE  112 — General  arrangement  of  Telefunken  radio  frequency  alternator. 

ing  instead  of  opposing  each  other,  there  will  be  produced  in  the  second- 
ary circuit  an  electromotive  force  of  triple  frequency.  Thus  the  same 
equipment  can  be  readily  used  either  as  a  doubler  or  a  tripler. 

A  clear  idea  of  the  interior  construction  of  the  Telefunken  radio 
frequency  alternators  can  be  obtained  from  Figure  112.  The  left  hand 
portion  of  the  figure  gives  a  vertical  cross  section  of  half  of  the  machine. 
Here  A  is  the  shaft  to  which  the  driving  motor  or  engine  is  attached 
either  directly  or  through  appropriate  gearing.  E  is  the  inductor  or 


Telefunken  Company — Arco  Alternator 


115 


rotor,  a  rotating  mass  of  steel,  on  the  outer  surface  of  which  are  cut  a 
great  number  of  grooves  parallel  to  A  thus  producing  the  longitudinal 
teeth  and  slots  indicated  in  cross  section  at  R  in  the  right  hand  portion 
of  the  figure.  The  constant  direct  current  passing  through  the  field  wind- 
ing, F  (which  is  an  ordinary  circular  coil  or  ring  of  square  cross  section), 
produces  a  field  the  lines  of  force  of  which  take  the  path  indicated  by 
the  dashed  line,  P.  It  will  be  seen  that  this  path  is  suitably  interlinked 
with  the  coil,  F,  and  passes  through  the  yoke,  Y,  the  stator  slot  supports 
W,  and  the  rotor,  R.  The  armature,  which  is  in  two  portions,  one  on  each 


FIGURE  113— Telefunken  Company  10  K.  W.,  10,000  cycle  alternator. 


side  of  the  field  coil  consists  of  to-and-fro  windings  in  longitudinal  slots 
parallel  to  those  of  the  rotor.  The  portions  of  the  armature  can  be  placed 
in  series  or  parallel  in  accordance  with  the  characteristics  of  the  circuit 
to  which  the  machine  is  connected.  The  mode  of  winding  the  armature  is 
indicated  at  W  in  the  right  hand  portion  of  the  figure.  It  is  evident 
that  as  the  rotor  revolves,  the  field  passing  through  the  armature  turns, 
W  pulsates  back  and  forth  with  a  frequency  corresponding  to  the  product 
of  the  number  of  rotor  slots  and  the  rotor  revolutions  per  second.  The 
advantage  of  this  (inductor)  type  of  machine  as  compared  to  those  with 


116         General  Electric  Company — Alexanderson  Alternator 

wound  armatures  is  that  the  rotating  portion  consists  of  a  solid  steel 
mass  and  is  consequently  much  more  sturdy  than  a  normal  armature 
carrying  wire  windings  on  a  laminated  support. 

The  appearance  of  a  small  (10  K.  W.)  machine  of  this  type  is  indi- 
cated in  Figure  113.  The  motor  is  mounted  at  the  front  of  the  base  plate 
and  the  alternator  at  the  rear.  The  housing  between  them  contains  the 
multiplying  gear.  The  motor  starter,  and  the  speed  controlling  rheostat 
are  mounted  on  the  wall  at  the  rear.  The  machine  shown  produced  10,000 
cycles  per  second  directly.  Its  use  in  radio  telephony,  together  with  the 


FIGURE  114 — General  Electric  Company — 
Alexanderson  alternator. 

other  portions  of  a  frequency  changer  set  of  which  it  was  a  part,  will  be 
described  under  "Control  Systems,"  on  page  190. 

Continuing  our  consideration  of  the  generation  of  radio  frequency 
currents  by  alternators,  we  pass  to  an  interesting  and  important  form  of 
alternator  largely  developed  by  Mr.  E.  F.  W.  Alexanderson  of  the  General 
Electric  Company.  This  machine  has  generally  been  distinguished  by  the 
direct  generation  of  the  very  high  frequency  desired,  and  its  construction 
has  given  rise  to  numerous  difficult  problems.  The  experimental  work  in 
connection  with  these  alternators  was  originally  undertaken  by  the  Gen- 


Alexanderson  Alternator — Early  Forms  117 

eral  Electric  Company  at  the  suggestion  of  Mr.  R.  A.  Fessenden,  then 
associated  with  the  National  Electric  Signaling  Company ;  and  much  of 
the  earlier  development  was  done  in  conjunction  with  that  company. 

In  1908,  Mr.  Alexanderson  described  a  100,000  cycle  alternator  of 
this  type,  built  to  deliver  approximately  2  kilowatts.  A  later  description 
given  by  him  follows  (with  brief  additions  by  the  Author)  : 

"The  alternator  is  of  the  inductor  type  (that  is,  with  stationary 
armature  and  field,  but  with  a  rotating  element  which  causes  a  pulsating 
field  to  cut  the  armature  conductors),  and  is  provided  with  a  novel  ar- 
rangement of  the  magnetic  circuit,  allowing  the  construction  of  a  rotor 
which  can  be  operated  at  exceedingly  high  speeds.  In  the  final  form  of 
the  alternators,  shown  in  Figure  114,  the  rotor,  C,  consists  of  a  steel  disc 
with  a  thin  rim  and  much  thicker  hub,  shaped  for  maximum  strength 


FIGURE  115 — Rotor  and  shaft  of  100,000  cycle  Alexanderson  alternator. 

(that  is,  with  a  width  that  progressively  diminishes  from  the  shaft  out, 
so  that  the  outward  strain  on  the  material  because  of  centrifugal  force 
is  the  same  from  the  shaft  to  outer  rim).  The  field  excitation  is  pro- 
vided by  two  coils,  A,  located  concentric  with  the  disc  and  creating  a 
magnetic  field  the  lines  of  force,  F,  of  which  pass  through  the  cast  iron 
frame,  D,  the  laminated  armature  support,  B  and  E,  with  its  teeth,  and 
the  disc,  C.  This  flux  also  passes  through  the  narrow  air  gaps  on  each 
side  of  the  disc  rotor,  and  is  indicated  in  the  figure  by  the  dashed  line 
with  arrows.  B  represents  the  two  armatures  which  are  secured  in  the 
frame  by  means  of  a  thread,  in  order  to  allow  an  adjustment  of  the  air- 
gap,  the  laminations  carrying  the  armature  conductors  being  located  at 
E.  Instead  of  poles  or  teeth,  the  disc,  C,  is  provided  with  slots  which  are 
milled  through  the  thin  rim  so  as  to  leave  spokes  of  steel  between  the 


118  Alexanderson  Alternator 

slots.  The  slots  are  filled  with  a  non-magnetic  material  (phosphor  bronze) 
which  is  riveted  in  place  solidly,  in  order  to  stand  the  centrifugal  force 
and  to  provide  a  smooth  surface  on  the  disc  so  as  to  reduce  air  friction. 
The  centrifugal  force  on  each  slot  filler  is  no  less  than  eighty  pounds 
(37  kg.)  at  the  high  speed  at  which  the  machine  is  run. 

"The  standard  100,000  cycle  rotor  of  chrome  nickel  steel  with  300 
slots  is  shown  in  Figure  115."  The  shaft  bearings  are  clearly  visible  at 
the  ends,  and  it  will  be  seen  that  they  are  arranged  so  as  to  make  forced 
oiling  practicable.  The  shaft  in  this  type  of  alternator  is  long  and  flex- 
ible, thus  permitting  the  rotor  to  center  itself  and  rotate  about  its  center 
of  mass  somewhat  as  is  done  in  the  case  of  centrifugal  dryers  for  laun- 
dries. In  this  way,  excessive  shaft  strains  are  avoided.  There  are  certain 
speeds  (1,7QO  and  9,000  R.  P.  M.)  for  which  the  shaft  and  rotor  pass 
through  their  own  resonant  periods  of  mechanical  vibration,  and  at  these 
speeds  marked  shaft  vibration  tends  to  occur. 

A  closer  view  of  a  portion  of  the  rotor,  showing  the  slot  fillers  of 
non-magnetic  material,  is  given  in  Figure  116.  Some  idea  of  the  care 


FIGURE  116 — Portion  of  rotor  of  Alexan- 
derson  100,000  cycle  alternator, 
showing  slots  in  disc. 

required  in  the  construction  of  such  a  machine  can  be  gained  from  the 
details  of  the  rotor  construction.  Since  the  speed  of  rotation  of  the  rotor 
is  20,000  revolutions  per  minute,  or  over  330  revolutions  per  second,  the 
actual  speed  at  the  rim  is  nearly  twelve  miles  per  minute !  Such  a  ma- 
chine must,  accordingly,  be  considered  a  masterpiece  of  engineering 
design.  (A  whimsical  calculation  has  been  made  which  shows  that  the 
rotor,  if  released  while  spinning  at  full  speed,  would,  if  it  maintained  its 
speed  thereafter,  roll  from  America  to  Europe  in  a  few  hours!) 

There  are  two  methods  of  armature  winding  employed  in  the  simpler 
forms  of  these  machines.     The  first  form,  which  is  a  simple  to-and-fro 


Alexanderson  Alternator 


119 


winding  (one  turn  per  slot)  is  shown  in  Figure  117.  In  this  form  of 
armature  there  are  600  slots  for  a  100,000  cycle  machine.  A  second  form 
of  winding  for  the  armature  has  only  400  slots  for  the  100,000  cycle 
machine.  It  is  shown  in  Figure  118,  and  really  consists  of  two  windings 


FIGURE  117— Portion  of  armature  winding  of  100,000 
cycle  Alexanderson  alternator;  600-slot  type. 

in  parallel  in  each  of  which,  by  a  sort  of  vernier  action,  a  300-slot  rotor 
field  produces  100,000  cycle  current  in  the  same  phase  in  each  of  the 
armature  windings.  It  is  possible,  using  an  SOO-slot  armature  winding 
of  the  last-mentioned  type,  to  produce  a  200,000  cycle  current  by  direct 


FIGURE  118— Portion  of  armature  winding  of  100,000 
cycle  Alexanderson  alternator;  400-slot  type. 

generation.    This  is  by  far  the  highest  frequency  which  has  as  yet  been 
produced  directly  by  an  alternator. 

Through  the  courtesy  of  John  L.  Hogan,  Jr.,  of  the  National  Electric 
Signaling  Company,  we  are  enabled  to  show  in  Figure  119  a  test  of  an 
early  form  of  80,000  cycle  alternator  built  by  the  General  Electric  Com- 
pany and  used  at  the  Brant  Rock  station  of  the  National  Electric  Signal- 
ing Company  in  1906.  This  machine  had  a  double  inductor  with  inward 


120 


Alexanderson  Alternator 


projecting  teeth  on  each  half,  and  the  stator  lay  between  the  two  "saucer'' 
shaped  inductors.  It  will  be  seen  that  this  machine  was  belt  driven  to 
get  the  proper  ratio  of  motor  to  alternator  speeds,  and  that  the  motor  is 
much  larger  than  the  alternator.  This  is  quite  explicable  when  it  is  re- 
membered that  the  windage  loss  in  these  machines  at  20,000  R.  P.  M.  is 
high,  it  having  been  claimed  that  the  rotor  is  actually  polished  either  by 
air  friction  or  by  the  friction  of  floating  dust  particles.  In  any  case,  the 


FIGURE  119 — Early  form  of  Alexanderson  alternator  under  test 

at  Brant  Rock  Station  of  National  Electric 

Signaling  Company. 

air  streaming  out  from  the  machine  is  appreciably  warmed.  This  wind- 
age loss  becomes  important  in  any  but  the  smallest  alternators  of  this 
type. 

A  somewhat  similar  machine  built  by  the  National  Electric  Signaling 
Company  in  1907  and  equipped  with  de  Laval  steam  turbine  drive  is 
shown  in  Figure  120.  This  has  the  advantage  that,  since  the  turbine  is 
itself  an  extremely  high  speed  machine,  the  gearing  losses  are  eliminated 
by  the  direct  drive.  Sufficiently  accurate  speed  regulation  of  a  steam 


Alexanderson  Alternator 


121 


BB 


FIGUKE  120 — Early  form  of  Alexanderson  alternator  coupled  to 

de  Laval  turbine ;  under  test  by  National 

Electric  Signaling  Company. 

driven  machine  is  secured  in  p'raqtice  by  maintaining  the  steam  pressure 
and  radio  frequency  load  at  constant  values.  The  gearing  shown  in  the 
figure  is  used  to  reduce  the  main  shaft  speed  in  the  ratio  of  l-to-10  for 
the  operation  of  the  turbine  governor.  It  will  be  noted  that  the  alter- 
nator in  this  figure  has  an  adjustment  to  rotate  each  armature  slightly 
relative  to  the  frame  so  as  to  bring  the  generated  currents  into  phase  and 
also  has  an  adjustment  whereby,  as  stated  previously,  the  armatures  may 
be  brought  nearer  to  or  further  from  the  rotor  for  precise  adjustment  of 
the  air  gap.  Such  an  adjustment  is  of  importance  since  the  output  of 


FIGURE  121 — Intermediate  type  of  Alexanderson  alternator. 


122  Alexanderson  Alternator 

the  machine  is  largely  dependent  on  the  air  gap,  and  a  very  small  air 
gap  (of  5  or  10  thousandths  of  an  inch,  or  an  eighth  to  a  quarter  of  a  milli- 
meter) is  of  advantage.  The  usual  gap  is  0.015  inch  (0.38  mm.)  with  a 
generated  voltage  of  150,  although  voltages  asrhigh  as  300  can  be  obtained 
with  a  0.004  inch  gap. 

This  machine  was  in  almost  daily  use  at  Brant  Rock  for  several 
years,  and  ran  for  hours  at  a  time  without  attention.  The  maximum 
output  was  something  over  1  K.  W.  at  100,000  cycles. 

A  later  fqrm  of  a  2  K.  W.  Alexanderson  alternator  is  shown  in 
Figure  121.  This  set  shows  the  elaborate  forced-feed  oiling  system  which 
has  been  adopted  for  the  later  machines.  The  auxiliary  and  main  bear- 
ings to  the  right  of  the  rotor  are  clearly  visible. 

The  most  recent  form  of  2  K.  W.  machine  of  this  type  is  shown  in 
Figure  122.  The  oiling  system  in  this  machine  is  provided  with  an  inter- 


FIGURE  122 — Recent  type  of  2  K.V.A.,  100,000  cycle  Alexanderson  alternator. 

esting  protective  device.  The  oil  which  is  returned  to  the  reservoir  at 
the  right  of  the  base  plate  (the  tank  having  a  sheet  metal  cover  with 
handle)  strikes  a  small  pivoted  shovel.  Its  weight  depresses  this  shovel 
against  a  controlling  spring  tension.  Should  the  flow  of  oil  cease  for  any 
reason,  the  shovel  flies  up  and  automatically  ope.n^;  the  driving  motor 
circuits.  In  this  way,  any  danger  of  j$8tlevd  bearings  ''freezing"  is 
obviated.  In  this  set,  the  alternator  is  driven  by  a  110  or  220- volt,  direct 
current,  shunt  motor  with'  commutating  poles.  The  motor  speed  is  2,000 
revolutions  per  minute  and  this  is  raised  to  the  requisite  20,000  revolu- 
tions per  minute  by  the  l-to-10  helical-cut  gearing  enclosed  in  the  housing 
at  the  center  of  the  base.  The  oil  pump,  which  is  chain  driven  from  the 
motor  shaft,  is  shown  at  the  right  hand  corner  of  the  base.  To  prevent 
any  possibility  of  binding  between  the  two  thrust  bearings,  due  to  ex- 
pansion of  the  shaft  because  of  heating,  the  machine  is  provided  with  a 


Alexanderson  "Gyro"  Alternator    5  123 

system  of  equalizing  levers  to  compensate  for  such  shaft  heating.  These 
levers  are  shown  in  the  left  front  of  Figure  122  with  the  elastic  con- 
trolling leaf  between  them.  Any  tendency  which  would  cause  a  change 
in  air  gap  is  counteracted  by  the  automatic  action  of  the  levers.  If  the 
air  gap  should  tend  to  change  at  either  side,  the  magnetic  attraction  at 
that  side  would  cause  an  additional  pressure  and  consequent  heating  on 
the  thrust  bearings  at  that  end ;  and  a  consequent  expansion  of  the  shaft 
there  would  bring  the  rotating  disc  back  to  a  central  position. 

The  expansion  of  the  shaft  by  temperature  is  thus  taken  advantage 
of  to  insure  a  correct  alignment.  The  usual  output  of  these  alternators 
is  from  10  amperes  at  200  volts  to  20  amperes  at  100  volts,  depending 
on  the  nature  of  the  load  and  the  mode  of  internal  connection  of  the 
armature  sections  of  the  machine.  The  effective  resistance  of  the  arma- 
ture is  1.2  ohms,  the  inductance  being  8.6  microhenrys  corresponding  to 
5.4  ohms,  at  a  frequency  of  100,000  cycles,  or  wave  length  of  3,000  meters. 
The  resonance  condenser  load  would,  therefore,  be  0.29  microfarad  at 
the  frequency  mentioned,  if  no  loading  coil  were  used  external  to  the 
machine. 

Another  recent  type  of  Alexanderson  radio  frequency  alternator  is 
the  so-called  "gyro  alternator. "  The  designation  is  based  on  the  simi- 
larity of  bearings  in  the  machine  in  question  and  those  in  a  high  speed 
gyroscopic  compass.  A  heavy  shaft  is  used,  so  that  vibration  at  the 
"critical  speeds"  does  not  occur,  these;  speeds  being  much  higher  than 
those  at  which  the  machine  is  actually  run.  The  use  of  ball  bearings  in 
this  machine  has  simplified  the  construction.  No  auxiliary  bearings  are 
needed  in  this  machine.  J 


FIGURE  123 — Recent  General  Electric  Company- Alexanderson  alternator  of  "gyro' 

type. 


124  Alexanderson  High  Power  Alternator 


tor 


Figure  123  shows  one  of  these  machines  with  belted  driving  mo 
and  all  auxiliaries  needed  for  a  complete  radiophone  equipment  mounted 
on  a  base.  The  particular  equipment  shown  has  been  ined  under  favor- 
able conditions  for  the  transmission  of  speech  160  miles  (250  km.),  be- 
tween Schenectady  and  the  Author's  laboratory  in  New  York.  The 
alternator  generates  33,000  cycles  per  second,  which  is  transformed  into 
100,000  cycles  (corresponding  to  a  wave  length  of  3,000  m.).  The  100,- 
000  cycle  energy  is  modulated  by  a  magnetic  amplifier  which  is  controlled 
directly  by  a  standard  microphone.  A  description  of  the  magnetic  ampli- 
fier system  of  modulation  follows  under  ''Modulation  Control  Systems," 
page  195. 

Passing  from  the  smaller  machines,  Mr.  Alexanderson  has  had  built 
a  50  kilowatt,  50,000  cycle  alternator  (and  very  considerably  larger 
machines  are  under  test  and  construction).  This  machine  is  shown  in 
Figure  124.  The  open  circuit  voltage  of  this  machine  and  the  trans- 


FIGUKE  124 — 50  kilowatt,  50,000  cycle,  General  Electric  Compaiiy-Alexanderson 

alternator. 


former  described  below  is  about  550  volts,  but  the  machine  is  normally 
operated  at  about  125  amperes  and  400  volts.  The  rotor  is  similar  to, 
although  naturally  larger  than 'that  of  the  smaller  machines  previously 
describet^lmt  an  extremely  heavy  and  rigid  shaft  is  used.  The  machine 
has  proveiT  capable  of  furnishing  8§*  kilowatts  for  brief  periods.  Oper- 
ating at  3,500  revolutions  per  minutef  its  bearings  and  shaft  construction 
are  .similar  to  those  of  normal  high  speed  turbines.  The  machine  speed 
never  .attains  the '"  critical  speed"  value,  thus  avoiding  the  necessity  for 
auxiliary  bearings.  Because  of  the  very  rigid  shaft,  the  rotor  is  not 
measurably  deflected  by  the  magnetic  field.  "The  thrust  bearings  for 


Alexanderson  Alternator  and  Output  Transformer  125 

the  collars  shown  at  each  end  of  the  rotor  shaft  are  held  in  position  with 
a  system  of  equalizers,  which  have  for  their  object  the  avoidance  of  any 
possibility  of  binding  in  the  bearings  due  to  expansion  of  the  shaft  from 
change  in  temperature,  and  at  the  same  time  automatically  draw  up  all 
slack  in  the  bearings  as  they  become  worn.  The  equalizers  are  the  heavy 
vertical  columns  and  links  shown  in  the  photograph  of  the  assembled 
machine. 

"The  direct  generation  of  radio  frequencies  by  a  machine  working 
on  the  principle  of  a  simple  alternator  is  possible  only  by  the  use  of  a 
very  low  voltage  winding.  On  the  other  hand,  if  the  alternator  wind- 
ings were  designed  to  be  connected  directly  in  series  with  an  antenna,  the 
terminal  voltage  would  be  about  2,000  to  3,000  volts.  Thus  it  is  apparent 
that  with  this  type  of  machine  it  is  necessary  to  use  a  transformer  be- 
tween the  machine  and  its  output  circuit.  The  alternator  windings  con- 
sist of  thirty-two  independent  circuits  connected  to  the  same  number  of 
independent  primaries  of  the  transformer.  The  transformer  has  a 
number  of  secondary  circuits  which  can  be  connected  for  various  ratios 
of  transformation  between  4-to-l  and  24-to-l.  Thus  the  alternator  can 
be  adapted  to  antennas  of  greatly  different  characteristics.  The  primary 
windings  of  the  transformer  are  grounded  in  the  middle,  so  that  the 
greatest  potential  difference  to  ground  on  the  alternator  winding  is  one- 
half  the  voltage  generated  by  one  alternator  circuit. 

"The  transformer  is  a  closely  coupled  one,  the  coupling  coefficient 
being  0.95.  In  the  phraseology  of  the  alternating  current  designers,  the 
transformer  may  be  described  as  having  about  30  per  cent,  magnetizing 
current  and  30  per  cent,  total  leakage.  Although  the  transformer  has 
no  iron  core,  it  has  a  measurable  core  loss  due  to  the  eddy  currents  in  the 
conductors  caused  by  the  magnetic  flux.  If  it  were  not  for  these  eddy 
currents,  the  efficiency  of  the  transformer  would  be  close  to  99  per  cent. ; 
as  it  is,  the  efficiency  is  about  95  per  cent.  This  efficiency  is  approxi- 
mately constant  between  frequencies  of  25,000  and  50,000  cycles,  be- 
cause what  the  transformer  in  one  sense  gains  by  the  higher  frequency, 
it  loses  on  account  of  the  higher  eddy  current  accompanying  that  fre- 
quency. The  numerous  multiple  circuits  in  the  primary,  as  well  as  those 
in  the  secondary,  are  carefully  transposed  so  as  to  make  cross  currents 
impossible  between  the  different  circuits. 

"While  it  appears  that  the  most  practical  arrangement  from  all 
points  of  view  is  the  one  described,  i.  e.,  a  low  voltage  winding  and  trans- 
former, experiments  have  been  made  with  windings  distributed  in  such  a 
way  that  larger  slo|s  can  be  used  with  room  for  more  insulation.  A  sample 
machine  of  this  type  of  3  k.w.  output  at  45,000  cycles  was  built,  and  a 
diagrammatic  representation  of  the  armature  cross  section  and  rotor  is 
given  in  Figure  125.  This  generates  a  frequency  three  times  as  high  as 


126  Results  with  Alexanderson  Alternator 

the  One  for  which  the  slots  on  the  winding  are  apparently  designed. 
This  method  may  be  characterized  as  generating  triple  harmonics  without 
the  fundamental.  The  action  is  somewhat  like  that  of  a  vernier,  the  flux 
through  the  stator  projections  changing  from  that  due  to  two  teeth  on 
the  rotor  to  that  due  to  one  tooth  at  three  times  the  apparent  frequency 
of  the  machine.  While  the  characteristics  of  this  machine  have  proven 
entirely  satisfactory,  in  accordance  with  expectations,  it  is  probable  that 
the  original  simple  form  of  winding  will  be  adhered  to,  because  the  con- 
centration of  large  conductors  with  more  current  in  one  slot  causes  not 
only  higher  losses,  but  also  a  lower  rate  of  heat  dissipation  and  therefore 
less  output  can  be  expected  from  the  same  amount  of  material." 


FIGURE  125 — Diagrammatic  representation 

of  Alexanderson  alternator  for  direct 

generator  of  triple  frequency. 

It  may  here  be  mentioned  that  the  machines  shown  in  Figures  121, 
122,  123,  and  124  have  all  been  used  for  radio  telephony  in<  connection 
with  further  devices  which  will  be  described  under  "Control  Systems." 
The  first  was  used  principally  by  the  National  Electric  Signaling  Com- 
pany in  Mr.  Fessenden's  tests  between  Boston  and  New  York  (Jamaica), 
a  distance  of  some  150  miles  (240  km.).  This  was,  however,  not  a  matter 
of  regular  communication,  but  rather  of  test  work.  The  machine  shown 
in  Figure  122  has  enabled  quite  regular  communication  between 
Schenectady  and  New  York,  the  distance  being  150  miles  (250  km.). 
Even  the  smallest  machine  (of  Figure  123)  running  on  much  reduced 
power,  has  enabled  the  same  stretch  to  be  bridged  when  suitable  receiving 
apparatus  was  employed. 

With  the  large  machine  shown  in  Figure  124,  employing  the  mag- 
netic amplifier  controlling  device  to  be  described  hereafter,  the  output 
was  successfully  modulated  between  5.8  kilowatts  minimum  and  42.7 
kilowatts  maximum.  This  is,  to  date,  the  maximum  amount  of  radio 
frequency  energy  controlled  telephonically  by  any  means. 


CHAPTER  VI. 

(7).  MODULATION  CONTROL  IN  RADIO  TELEPHONY — (a) 
DEGREE  OF  CONTROL  ;  MODULATION  CHARACTERISTIC  ;  LINEAR 
AND  NoN-LlNEAR  MODULATION  CONTROL;  ACTUAL  CHAR- 
ACTERISTIC, (b)  STABILITY  OF  CONTROL;  STATIC  AND  DY- 
NAMIC CHARACTERISTICS,  (c)  RATING  OF  RADIOPHONE 
TRANSMITTERS,  (d)  TYPES  OF  CONTROL,  (e)  MICROPHONE 
TRANSMITTER  CONTROL;  SINGLE  MICROPHONE  CONTROL; 
MULTIPLE  MICROPHONE  CONTROL;  METHODS  OF  LORENZ 
COMPANY  AND  GOLDSCHMIDT;  METHOD  OF  DITCH  AM.  (f) 
HIGH  CURRENT  MICROPHONES;  FESSENDEN'S  TELEPHONE 
RELAYS;  CONDENSER  TRANSMITTERS  AND  METHOD  OF  USE; 
DUBILIER'S  RELAY;  BERLINER  COMPANY  HIGH  CURRENT 
MICROPHONE;  EGNER-HOLMSTROM  HIGH  CURRENT  MICRO- 
PHONE; ScHEiDT-BooN  MARZI  MICROPHONE;  CHAMBER'S 
LIQUID  MICROPHONE  ;  VANNI'S  LIQUID  TRANSMITTER  ;  MAJOR- 
ANA'S  LIQUID  TRANSMITTER  AND  EXPERIMENTS  THEREWITH. 

7.  MODULATION  CONTROL  IN   RADIO  TELEPHONY. 

We  have,  up  to  this  point,  considered  many  matters  which  are  com- 
mon to  radio  telephony  and  radio  telegraphy  since  the  sustained  wave 
generating  systems  are  naturally  applicable  to  the  latter  field  as  well  as 
the  former  and  indeed  were  originated  principally  in  connection  with 
telegraphy.  We  pass  now,  however,  to  a  matter  exclusively  related  to 
radio  telephony,  namely  the  modulation  or  control  of  amounts  of  power 
varying  from  a  few  watts  to  many  kilowatts  by  the  human  voice.  The 
problem  is  indeed  a  difficult  one,  and  for  a  long  time  practically  defied 
solution.  When  it  is  considered  that  the  rate  of  energy  radiation  in  the 
form  of  sound  in  ordinary  speech  is  of  the  order  of  one  one-hundred- 
millionth  to  one-billionth  (0.00000001  to  0.000000001)  of  a  watt  and 
that  the  delicate  and  excessively  complex  variations  of  the  sound  energy 
must  be  faithfully  reproduced  with  an  energy  amplification  of  hundreds 
of  billions,  and  that  the  energy  to  be  modulated  is  of  the  peculiar  form 
associated  with  radio  frequency  currents,  the  difficulties  of  the  problem 

127 


128 


Degree  of  Control 


become  evident.     And  yet  radio  telephony  is  entirely  dependent  on  the 
simple  solution  thereof. 

Before  describing  in  detail  the  various  methods  of  modulation  con- 
trol which  have  been  devised,  we  shall  consider  certain  broader  questions 
connected  therewith.  The  first  of  these  is  the  completeness  of  control 
systems. 

(a)  DEGREE   OF   CONTROL. 

In  every  radiophone  transmitter,  there  is  some  point  at  which  a  con- 
trolling current,  voltage,  inductance,  capacity,  or  resistance  exists.  The 
current  might  be,  for  example,  the  fluctuating  current  in  a  telephone 
transmitter  circuit.  The  voltage  might  be  the  voltage  applied  to  the  grid 


—  Current  tor  Max/mum 
Output 


• —  yg  Mar/mum  Current 
~TC ~%  Maximum  Current 


0 


Control  Current 


FIGURE   126 — Complete  linear  modulation 
control  curve. 

of  a  vacuum  tube  of  some  sort,  this  voltage  being  derived  from  the 
secondary  circuit  of  a  transformer  connected  in  a  microphone  transmitter 
circuit.  The  resistance  might  be  the  resistance  of  a  microphone  placed 
directly  in  the  antenna  of  a  radiophone  transmitter.  Whatever  the  con- 
trolling element,  it  must  vary  between  certain  extreme  values  when 
speech  is  being  transmitted,  these  limits  being  reached  for  the  peaks  of 
the  loudest  sounds  which  are  encountered  in  ordinary  speech.  Indeed, 
it  is  preferable  that  these  peaks  should  be  reached  for  such  normal  speech 
rather  than  for  shouting  since  otherwise  the  control  tends  to  be  weak 
and  excessive  amplifications  may  be  required  somewhere  in  the  set. 

In  Figure  126  we  have  a  control  characteristic  of  a  desirable  sort. 
Horizontally  is  plotted  the  controlling  element  (current,  voltage,  ca- 
pacity, inductance,  resistance,  or  a  combination  of  these),  this  element 
varying  between  zero  and  the  value  0  D.  Vertically  are  plotted  values 


Incomplete  Control  Characteristics 


129 


of  the  controlled  or  antenna  radio  frequency  current,  this  varying  be- 
tween zero  and  CD.  It  will  be  seen  that  we  have  a  straight  line  char- 
acteristic curve;  that  is,  the  controlled  current  is  proportional  to  the 
controlling  current.  Furthermore,  the  control  is  complete,  since  we  as- 
sume that  the  current  CD,  is  the  greatest  current  which  the  sustained 
generator  is  capable  of  putting  into  the  antenna;  or,  in  other  words,  the 
current  CD  is  determined  by  the  actual  maximum  possible  output  of  the 
alternator,  arc,  radio  frequent  spark  transmitter,  or  vacuum  tube  trans- 
mitter used. 

The  question  arises  as  to  what  will  be  the  ammeter  reading  in  the 
antenna  when  no  speech  is  being  sent  out.  This  depends  on  whether  we 
choose  to  have  this  point  as  that  of  half  current  or  of  half  energy.  In 
the  former  case,  the  current  will  center  around  the  point  F  which  repre- 
sents one-half  the  maximum  current.  In  the  latter  case,  the  current  will 
rise  and  fall  about  the  point  E  which  represents  the  reciprocal  of  the 
square  root  of  two  (that  is,  0.707)  times  the  maximum  current.  Under 
normal  conditions  of  speech,  in  some  types  of  radiophone  (particularly 
those  with  stable  control  to  be  described  hereafter)  the  antenna  ammeter 
does  not  change  markedly  from  the  point  E  (or  F)  when  one  actually 
carries  on  conversation.  In  other  types  (and  especially  those  with  un- 
stable control)  the  average  current  in  the  antenna  may  change  consid- 
erably when  speech  is  being  transmitted. 

A  curve  representing  incom- 
plete control  is  given  in  Figure 
127.  It  will  be  noted  that  the  en- 
tire available  variation  in  the  con- 
trolling element  will  cause  a  vari- 
ation in  the  antenna  current  only 
between  the  values  OG  and  DA 
and  not  between  zero  and  the  max- 
imum available  current  CD.  In 
this  case  we  may  define  the  per- 
centage of  control  as  the  quotient 
of  AB  divided  by  CD.  Such  a 
radiophone  set  with  a  normal 
linearly  proportional  receiver  will 
be  equivalent  to  a  considerably 

^^  less    powerful    transmitter    than 

that  represented  in  Figure  126. 

The  Author  advocates  control  characteristics  in  which  the  micro- 
phone current  is  taken  as  the  controlling  element  and  the  antenna  cur- 
rent as  the  controlled  element.  First  of  all,  these  elements  are  fairly 


v- 

Current  for  ^fojri/nt//f9 

1 

, 

X<? 

D 

0 

Control  Current  '  farlfa/fage) 

FIGURE  127 — Incomplete  linear  modu- 
lation control  curve. 


130 


Stability  of  Control 


I 


Current  fo 


readily  measurable.  In  the  second  place,  what  is,  after  all,  desired  is 
that  the  current  variations  through  the  receiver  telephones  shall  be  pro- 
portional to  the  current  variations  in  the  microphone  transmitter  as  in 
an  ordinary  telephone  line.  It  is  accordingly  deemed  best  to  adhere  to 
current  control  Characteristics  throughout. 

In  practice,  the  perfect  type  of  control  characteristic  shown  in  Fig- 
ure 126  is  not  realized.    A  more  common  form  which  is  fairly  acceptable 

is  shown  in  Figure  128.  It  will 
be  seen  that  the  antenna  current 
never  falls  below  U  although  this 
leads  to  a  waste  of  energy.  From 
V  to  W  the  control  is  linear  and 
satisfactory,  but  at  W  it  flattens, 
remaining  at  constant  current  to 
X.  The  maximum  output  current 
is  never  reached,  the  mere  ex- 
istence of  the  controlling  element 
preventing  its  attainment. 

(b)    STABILITY   OF  CONTROL. 

The  control  system  of  a 
radiophone  may  be  classified  as 
stable  or  unstable  depending  on 

whether  the  points  on  the  upper  and  lower  portions  of  the  control  curve 

can  be  held  steadily  with  the  control  system  used  or  whether  they  can  be 

reached  for  only  a  brief  period  of  time.   The  simplest  example  of  a  stable 

control  system  would  be  the  following:  Imagine  a  radio  frequency  al- 
ternator, driven  by  a  constant 

speed  motor,  placed  directly  in  a 

tuned  antenna;  and  in  series  with 

the  alternator  and  directly  in  the 

antenna  a  microphone  transmitter 

(or  a  variable  resistance,  which 

is  its  equivalent).     It  is  evident 

that  the  system  is  perfectly  stable 

no  matter  what  the  value  of  the 

microphone  resistance,   since  the 

only  possible  effect  of  an  increase 

or  diminution  of  the  microphone 

resistance  is  to  lower  or  raise  the 

antenna    current.      The    control 


Control  Current 
(or  w 


FIGURE   128 — Typical   incomplete   non- 
linear modulation  control  curve. 


curve  of  such  a  system  would  be 


FIGURE  129 — Dynamic  characteristic  of 

falling  current  for  unstable 

control   system. 


Radiophone  Transmitter  Rating  131 

a  "static"  characteristic;  i.  e.,  one  for  stationary  conditions.  The 
simplest  example  of  an  unstable  control  system  would  be  the  following: 
A  Poulsen  arc  is  placed  directly  in  the  antenna  in  series  with  a  micro- 
phone (or  a  variable  resistance).  Changing  the  resistance  of  the  micro- 
phone will  not  merely  cause  the  antenna  current  to  change;  it  may 
actually  cause  the  extinction  of  the  arc  altogether,  if  the  inserted  resist- 
ance is  too  high.  So  that  the  system  would  be  unstable  at  this  limit. 
This  is  illustrated  in  Figure  129  where  the  antenna  circuit  is  plotted 
against  time.  The  current  remains  constant  from  P  to  Q,  it  being  sup- 
posed that  the  resistance  in  the  antenna  is  moderate  for  this  range  of 
time.  At  Q  a  large  resistance  is  inserted  in  the  antenna,  for  example,  by 
speaking  into  the  microphone,  or  pulling  out  its  diaphragm.  The  antenna 
current  may  not  merely  decrease ;  it  may  rapidly  fall  to  zero  at  the  point 
V.  On  the  other  hand,  if  the  resistance  is  restored  to  its  former  small 
value  after  a  time  RT,  the  antenna  current  may  recover  the  full  value 
Q  rapidly.  In  other  words,  while  the  system  is  unstable  for  permanent 
changes,  it  may  be  operative  for  rapid  transient  changes  provided  these 
changes  are  of  very  short  duration.  For  this  case,  it  is  not  possible  to 
secure  a  complete  static  control  characteristic ;  dynamic  characteristics 
must  be  obtained  by  the  use  of  an  oscillograph  or  some  other  device  for 
following  the  rapidly  changing  antenna  and  controlling  currents. 

Generally  speaking,  unstable  control  systems  are  objectionable.  If 
the  time  RU  of  extinction  in  such  a  system  is  very  short,  then  a  low- 
pitched  sound  (of  relatively  long  period)  may  lead  to  complete  "break- 
ing" or  extinction.  On  the  other  hand,  if  the  time  RU  is  long  and  the 
slope  of  QSU  less  abrupt,  there  will  be  sluggishness  of  control  and  a  blur- 
ring or  muffling  of  speech.  Rigid  and  stable  control  is  desirable. 

(c)  RATING  OF  RADIOPHONE  TRANSMITTERS. 

In  a  receiving  set,  when  audibility  measurements  are  being  made  on 
received  speech  (on  the  basis  of  just  hearing  sound  of  any  character),  it 
is  the  maximum  transmitter  current  (CD  of  Figure  126)  which  is  being 
considered.  Consequently  the  Author  recommends  that  radiophone  trans- 
mitters be  rated  on  the  basis  of  maximum  energy  radiated,  corresponding 
to  maximum  current.  Here  100  per  cent,  control  is  assumed.  If  less 
than  full  control  is  attained,  the  rating  of  the  transmitter  should  be  the 
maximum  energy  variation.  As  has  been  stated,  for  unstable  control 
systems,  this  requires  an  oscillograph  for  the  determination  of  rating; 
but  generally  we  may  assume  the  maximum  energy  in  this  case  to  be  twice 
the  average  or  steady  value,  if  the  control  is  known  to  be  linear.  Many 
unstable  control  systems  flatten  out  in  control  (as  at  WX  in  Figure  128) 
for  high  currents,  and  consequently  their  rating  may  be  much  less  than 
that  given  by  the  double  energy  rule  above. 


132  Types  of  Control 

In  rating  radiophone  transmitters  on  the  basis  of  maximum  energy 
radiation,  it  must  be  understood  that  this  does  not  imply  that  a  1  K.  W. 
radiophone  transmitter  will  enable  the  clear  transmission  .of  speech  for 
the  same  distance  as  a  1  (antenna)  K.  W.  spark  transmitter  will  enable 
the  transmission  of  telegraphic  signals.  More  than  just  the  peaks  of  the 
received  speech  is  required  for  comprehensibility,  so  that  the  received 
speech  must  be  considerably  more  than  once  audibility  to  be  fully  under- 
stood. .The  exact  number  of  times  audibility  required  for  satisfactory 
speech  is  not  precisely  determined  at  present  and  depends  naturally  on 
the  freedom  from  speech  distortion.  It  is  probably  not  less  than  2  nor 
more  than  10. 

(d)  TYPES  OF  CONTROL. 

Control  systems  may  further  be  classified  as  absorption  systems  or 
generator  voltage  (or  current)  control  systems.  The  simplest  instance 
of  an  absorption  system  is  the  plain  microphone-in-antenna  modulation 
where  the  microphone  actually  absorbs  intermittently  a  considerable  por- 
tion of  the  radio  frequency  generator  output.  Such  systems,  while  dis- 
tinguished by  their  simplicity  and  satisfactory  behaviour  for  small  powers 
are  not  so  easy  to  apply  to  large  powers  because  of  the  difficulty  of 
absorbing  considerable  amounts  of  energy  in  any  system  sufficiently 
delicate  to  follow  the  voice  inflections.  Among  exceptions  to  this  state- 
ment, however,  are  the  vacuum  tube  absorptive  systems  to  be  described 
hereafter. 

The  generator-voltage  control  type  is  well  illustrated  by  the  use  of 
radio  frequency  alternator  in  the  antenna,  the  field  of  the  alternator 
being  excited  by  the  microphone  current  and  the  alternator  being  driven 
by  a  constant  speed  motor.  It  will  be  seen  that  the  generator  output  is 
variable  in  this  case,  and  not  constant  as  in  the  former.  This  requires 
quite  special  driving  motors  and  is  an  objection.  On  the  other  hand,  the 
absorption  control  systems  tend  to  be  constant  load  systems  and  do  not 
require  special  driving  machinery.  However,  unless  an  absorption  sys- 
tem is  carefully  devised,  it  may  be  uneconomical  of  energy,  since  it  is 
desirable  to  avoid  having  full  load  on  all  machinery  regardless  of  whether 
speech  is  being  transmitted  or  not. 

(e)  MICROPHONE  TRANSMITTER  CONTROL. 

An  ordinary  microphone  transmitter  of  high  resistance  will  carry  a 
steady  current  of  from  0.1  to  0.2  ampere  at  an  applied  voltage  of  10 
volts.  Its  resistance  is  therefore  of  the  order  of  50  to  100  ohms,  and  the 
•energy  which  it  can  absorb  steadily  is  about  2  watts.  If  it  is  attempted 
to  pass  more  current  than  that  mentioned  through  the  microphone,  a 
""frying"  or  crackling  sound  will  be  heard  in  the  receiver,  the  carbon 


Simple  Microphone  Control 


133 


grains  of  the  transmitter  will  overheat  and  burn,  and  the  microphone 
will  steadily  deteriorate.  A  so-called  "low  resistance"  transmitter  will 
carry  0.4  to  0.5  ampere  and  have  a  resistance  of  from  10  to  20  ohms. 
It  can  absorb  satisfactorily  but  little  more  energy  than  the  high  resist- 
ance form. 


FIGURE   130 — Various   arrangements   for   microphone   modulation   of  radiophone 

transmitter. 

When  a  microphone  overheats  from  the  passage  of  excessive  current,, 
which  is  very  likely  to  occur  when  the  over-enthusiastic  radiophone  ex- 
perimenter places  it  in  the  antenna  circuit  and  attempts  gradually  to 
increase  the  antenna  current,  it  "packs".  That  is,  the  grains  of  carbon 
expand  and  become  tightly  wedged  in  the  carbon  chamber  and  the  micro- 
phone no  longer  responds.  It  then  becomes  necessary  to  shake  the  micro- 


134  Most  Effective  Control 

phone  mechanically  to  release  the  grains  and  restore  its  modulating 
power.  In  one  form  of  radiophone  made  by  Dr.  de  Forest,  the  shaking 
of  the  microphone  was  accomplished  by  fastening  a  buzzer  to  it  and 
closing  the  battery  circuit  of  the  buzzer  occasionally.  The  resulting 
vibration  gave  the  desired  result.  A  more  simple  means  of  accomplishing 
the  same  result  is  by  tapping  the  transmitter.  A  * '  packed ' '  transmitter 
rapidly  deteriorates  through  overheating  and  burning  of  the  carbon 
grains. 

Dr.  Georg  Seibt  has  shown  that,  in  order  that  the  loudest  signal 
shall  be  heard  in  the  receiving  station  when  a  microphone  transmitter  is 
used  for  modulating  the  transmitted  energy,  a  simple  condition  must  be 
fulfilled.  It  is  that  the  resistance  (as  determined  by  energy  absorption 
of  the  microphone  when  undisturbed)  shall  be  equal  to  the  total  resist- 
ance (as  determined  by  energy  absorption)  of  the  remainder  of  the  radio 
frequency  circuits  of  the  transmitter.  For  example,  imagine  an  antenna 
of  8  ohms  total  resistance  (including  ohmic  resistance,  ground  resistance, 
radiation  resistance,  and  eddy  current  loss  resistance)  with  an  inserted 
microphone.  The  microphone  resistance  should  also  be  8  ohms.  From 
this  it  is  fairly  obvious  that  a  high  resistance  microphone  is  inapplicable, 
unless  it  is  not  in  the  antenna  but  so  coupled  or  connected  to  antenna 
circuit  (directly,  inductively,  or  capacitively)  that  its  effect  is  the  same 
as  if  a  smaller  resistance  equal  to  the  antenna  system  resistance  had  been 
inserted. 

We  show  in  Figure  130  a  number  of  arrangements  which  have  been 
used  for  the  direct  control  of  the  radiated  energy  by  a  microphone. 
Diagram  a  shows  the  microphone  inserted  in  the  direct  current  supply 
leads  of  the  arc,  thus  causing  appropriate  variations  of  the  arc  current 
and  arc  output.  Diagram  &  is  somewhat  different  in  that  alternating 
electromotive  forces  are  impressed  on  the  arc  as  well  as  the  constant 
supply  voltage.  The  alternating  voltages  are  transferred  to  the  arc 
supply  circuit  through  the  transformer  T  connected  to  the  microphone 
circuit  and  supply  circuit.  This  arrangement  is  due  to  Mr.  E.  Ruhmer. 
In  the  Diagram  c  the  microphone  has  been  transferred  to  the  oscillating 
circuit  of  the  arc.  This  method  would,  except  with  very  low  resistance 
microphones,  be  an  unstable  control  system.  In  Diagram  d,  which  shows 
a  circuit  used  by  both  Professor  V.  Poulsen  and  the  Telefunken  Com- 
pany, the  microphone  is  shunted  across  the  antenna  coupling  and  tuning 
coil.  It  would  therefore  act  to  detune  the  antenna  circuit  as  well  as  to 
absorb  energy  intermittently.  The  method  is  quite  effective.  Diagram 
e,  which  is  another  arrangement  due  to  Professor  Poulsen,  accomplishes 
the  same  results  by  coupling  the  microphone  inductively  to  the  antenna 
coupling  coil.  The  only  purpose  of  the  battery  in  this  case  is  to  bring 


Lorenz  Company  Multiple  Microphone  Control 


135 


the  microphone  resistance  (which  depends  on  the  current  passing  through 
it)  to  a  desired  value.  Diagram  /  illustrates  an  arrangement  used  by 
Mr.  Fessenden  (principally  with  radio  frequency  alternators  as  gen- 
erators) and  others.  In  this  simple  case  the  microphone  is  directly  in  the 
antenna,  and  moulds  the  radio  frequency  current  into  the  desired  speech 
form  envelope  more  or  less  fully.  Diagram  g  shows  the  unusually  elab- 
orate arrangement  adopted  for  modulation  by  Messrs.  Colin  and  Jeance. 
A  tuned  circuit  of  desired  constants  is  directly  coupled  to  a  portion  of 
the  antenna  coupling  coil.  The  microphone  is  directly  inserted  in  the 


FIGURE  131— C.  Lorenz  Company  multiple 
transmitter. 

tuned  shunting  circuit  which  has  sometimes  been  characterized  as  a 
*  *  spill-over ' '  circuit. 

Iii  order  to  modulate  more  energy  than  can  be  properly  handled  by 
one  microphone,  the  idea  was  originated  of  using  several  in  series,  low 
resistance  microphones  being  thus  employed,  The  idea  is  feasible  to  a 
limited  extent,  but  rapidly  leads  to  difficulties  in  carrying  the  energy  of 
the  speech  to  the  diaphragms  of  many  microphones.  An  extreme  instance 
of  this  method  is  shown  in  Figure  131,  which  shows  no  less  than  25 
Berliner  microphones  being  thus  used  by  the  C.  Lorenz  Company.  A  less 
extreme  instance  is  illustrated  in  the  radiophone  set  illustrated  in  Figure 
21  of  this  book,  which  shows  six  microphones  in  series.  It  is  desirable 
in  such  arrangements  to  have  the  paths  from  the  mouth  of  the  speaker 
to  the  different  microphones  of  equal  length  and  as  nearly  as  possible 
geometrically  identical,  so  that  each  microphone  gets  full  excitation. 


136 


Control  System  of  Ditcham;  of  Goldschmidt 


A  further  expedient  is  to  have  more  than  one  set  of  microphones 
available,  and  to  change  over  from  one  set  to  the  next  whenever  consider- 
able heating  occurs.  Data  is  not  available  as  to  the  practicability  of  this 
scheme,  but  it  seems  to  be  of  some  advantage. 

The  multiple  microphone 
transmitter  on  this  principle  em- 
ployed by  Lieutenant  Ditcham  is 
shown  in  Figure  132.  It  consists 
of  four  pairs  of  two  microphones 
each,  the  microphones  in  the  indi- 
vidual pair  being  simultaneously 
actuated  by  the  voice  and  con- 
nected in  series.  A  knob  on  the 
side  of  the  holder  (or,  in  some 
types  of  the  apparatus,  an  auto- 
matic push-button  arrangement) 
enables  changing  from  one  set  of 
microphones  to  the  next  about 
every  two'  minutes;  thus  preventing 
overheating.  Antenna  current  up 
to  10  amperes  have  thus  been  han- 
dled without  overheating  of  the 
microphones  arid  consequent  deter- 
ioration of  articulation. 
Mr.  R.  Goldschmidt  has  devised  a  method  of  using  several  micro- 
phones in  parallel.  Normally  this  is  not  feasible,  since  if  one  begins  to 
get  more  current  than  the  remainder  its  resistance  will  rapidly  fall  and 
it  will  soon  carry  the  entire  current,  thus  leading  to  injurious  overheat- 
ing. The  simplest  form  of  the  method  mentioned  is  given  in  Figure  133. 
As  will  be  seen,  the  microphones  are  each  in  series  with  a  coil  (L±  and 
L2  respectively).  The  coils  in  question  are  wound  oppositely  on  a  com- 


FIGURE  132 — Ditcham  multiple  micro- 
phone transmitter. 


FIGURE  133 — R.  Goldschmidt's  method  of  utilizing  microphones  in  parallel. 


Fessenden's  High  Current  Microphone  137 

mon  core.  As  long  as  the  current  through  each  microphone  is  the  same, 
equal  currents  will  now  through  each  coil  and  the  net  inductance  in  the 
circuit  will  be  zero.  If,  however,  one  of  the  microphones  takes  more 
current  than  the  other,  the  balancing  current  begins  to  circulate  in  the 
circuit  L1M1M>2L2  and  encounters  a  high  inductance  in  L±L2  since  it  does 
not  flow  in  the  opposite  direction  in  the  two  coils.  The  method  of  ex- 
tending the  idea  to  three  microphones  is  also  illustrated.  Here  coils  Lt 
and  L  are  wound  on  the  same  core,  as  also  are  the  coils  L2  and  L',  and 
the  coils  L3  and  L". 

(f)  HIGH  CURRENT  MICROPHONE  CONTROL. 

The  first  thought  that  naturally  suggests  itself  in  connection  with 
the  securing  of  microphones  that  will  modulate  successfully  more  energy 
than  wdll  the  ordinary  carbon  microphone  is  to  replace  the  carbon  by 
some  more  permanent  and  less  inflammable  material.  Carborundum  has 
been  suggested  by  several  inventors,  but  it  cannot  be  said  that  any  data 
is  available  favoring  the  belief  that  the  expedient  was  successful. 

In  1906  and  1907  Mr.  R.  A.  Fessenden,  at  that  time  directing  the 
work  of  the  National  Electric  Signaling  Company,  devised  a  number  of 
microphone  transmitters  which  carried  heavy  currents  for  considerable 
periods  of  time.  He  also  developed  a  heavy  current  telephone  relay, 
which  permitted  controlling  considerable  current  by  means  of  smaller 
currents  originating  in  an  ordinary  microphone  circuit  or  coming  from 
a  telephone  line.  A  description  of  these  devices  in  his  own  words,  with 
added  comments  by  the  Author,  follows  :* 

' '  A  new  type  of  transmitter  was  therefore  designed  which  the  writer 
(Mr.  Fessenden)  has  called  the  'trough'  transmitter.  It  consists  of  a 
soapstone  annulus  to  which  are  clamped  two  plates  with  platinum 
iridium  electrodes.  Through  a  hole  in  the  center  of  one  plate  passes  a 
rod,  attached  at  one  end  to  a  diaphragm  and  at  the  other  to  a  platinum 
iridiuni  spade.  The  two  outside  electrodes  are  water-jacketed. 

''The  transmitter  requires  no  adjusting.  All  that  is  necessary  is 
to  place  a  teaspoonful  of  carbon  granules  in  the  central  space.  It  is  able 
to  carry  as  much  as  15  amperes  continuously  without  the  articulation 
falling  off  appreciably.  It  has  the  advantage  that  it  never  packs.  The 
reason  for  this  appears  to  be  that  when  the  carbon  on  one  side  heats 
and  expands,  the  electrode  is  pushed  over  against  the  carbon  on  the 
other  side,  thus  diverting  a  greater  portion  of  the  total  current  to  the 
cooler  side,  which  has  thus  been  made  of  smaller  resistance.  It  will  be 
noted  that  the  two  halves  of  the  carbon,  on  the  opposite  sides  of  the 
spade  diaphragm  are  in  parallel.  These  transmitters  have  handled 

•  -Troc.   A.   I.   E.   E.,"   June   29,    1908. 


138 


Fessenden's  Transmitting  Relay 


amounts  of  energy  up  to  one-half  horse  power  (375  watts),  and  under 
these  circumstances  give  remarkably  clear  and  perfect  articulation  and 
may  be  left  in  circuit  for  hours  at  a  time." 

Such  a  water-cooled  microphone,  built  to  carry  up  to  6  amperes 
continuously,  and  suitably  mounted,  is  illustrated  in  Figure  134. 


FIGURE  134 — National  Electric   Signaling 

Company-Fessenden  high  current 

transmitter. 

A  more  complex  and  extremely  interesting  device  is  shown  in  Fig- 
ure 135.  This  is*  "a  transmitting  relay  for  magnifying  very  feeble 
currents.  It  is  a  combination  of  the  differential  magnetic  relay  and  the 
trough  transmitter.  An  amplification  of  15  times  can  be  obtained  with- 
out loss  of  distinctness.  .  .  .  The  successful  amplification  depends 
on  the  use  of  strong  forces  and  upon  keeping  the  moment  of  inertia  of 
the  moving  forces  parts  as  small  as  possible.  Amplification  may  also  be 
obtained  by  mechanical  means,  but  as  a  rule  this  method  introduces 


*  "Proc.   A.   I.   E.   E.,"   June  29,    1908. 


Fessenden's  Line-to-Radio  Relay 


139 


scratching  noises  which  'are  very  objectionable  even  though  comparatively 
faint. "  The  amplifying  relay  shown  in  Figure  135  is  capable  of  handling 
15  amperes  in  its  output  side.  Thus  over  ten  years  ago  Mr.  Fessenden 
recognized  the  desirability  of  being  able  to  control  the  radiophone  trans- 
mitter from  a  wire  line,  and  this  relay  was  developed  to  enable  the 
desired  result  to  be  obtained. 


FIGURE  135 — Fesseiiden  heavy  current  telephone  relay. 


A  complete  radiophone  station  at  Brant  Bock  embodying  the  idea 
just  mentioned  is  illustrated  in  Figure  136.  Although  completed  in 
1906,  the  design  thereof  was  remarkably  advanced.  In  the  right  fore- 
ground are  seen  the  radio  frequency  alternator  and  its  driving  motor  and 
controlling  rheostats.  Directly  back  of  these  is  a  compressed  air  tuning 
condenser.  On  the  table  is  shown  a  normal  line  telephone  set  connected 
to  the  high  current  relay  which  controls  the  outgoing  energy.  In  addi- 
tion, at  the  reader's  left,  on  the  table  is  placed  a  portion  of  the  receiving 
set.  On  December  11,  1906,  a  demonstration  of  radio  telephony  was 
given  from  Brant  Rock  to  Plymouth,  Massachusetts,  a  distance  of  10 
miles  (16  km.).  Both  speech  and  music  were  transmitted.  In  addition, 


140 


Fessenden's  Brant  Rock  Experiments 


speech  was  transmitted  over  an  ordinary  wire  line  to  the  radio  station 
at  Brant  Rock,  relayed  automatically  to  the  radiophone,  transmitted  by 
radio  to  Plymouth,  and  at  Plymouth  automatically  relayed  back  to  a 
wire  line.  Telephone  experts  present  noted  a  remarkable  absence  of 
distortion  of  speech  quality.  In  July,  1907,  speech  was  transmitted  be- 
tween Brant  Rock  and  Jamaica,  Long  Island,  a  distance  of  180  miles 
(290  km.)  over  land,  and  by  day.  The  antenna  mast  at  Jamaica  was 
180  feet  (55  m.)  high.  In  this  work,  "the  transmitting  relays  are  con- 


FIGUKE  136 — National  Electric  Signaling  Conipauy-Fessendeii  2  K.  W. 
radiophone  transmitter. 


nected  to  the  wire  line  circuit  in  the  same  way  as  the  regular  telephone 
relay,  except  that  in  place  of  being  inserted  in  the  middle  of  the  line,  they 
are  placed  in  the  radio  station  and  an  artificial  line  used  for  balancing. 
There  is.  no  difficulty  met  with  on  the  radio  side  of  the  apparatus,  but  on 
the  wire  line  there  are  the  well-known  difficulties  due  to  unbalancing 
which  have  not  been  entirely  overcome.  For  the  correction  of  these  diffi- 
culties, therefore,  we  must  look. to  the  engineers  of  the  wire  telephone 
companies.  At  present,  the  difficulties  are,  if  anything,  less  than  those 
met  with  in  relaying  on  wire  lines  alone. " 


Condenser  Transmitter 


141 


FIGURE    137 — ITessenden    condenser 
transmitter  for  radiophone  work. 


Another  form  of  transmitter  used 
by    Mr.    Fessenden    is    the    condenser 
transmitter.      This    is    not    a    carbon 
microphone  at  all,  but  a  variable  con- 
denser with  one  (or  more)  fixed  plates 
and  one  (or  more)  movable  plates,  the 
movable  plates  being  brought  nearer  to 
or  further  from  the  fixed  plates  by  the 
voice  vibrations.    In  this  way  there  are 
produced  in  this  condenser  changes  of 
capacity    closely    proportional    to    the 
sound  amplitudes.    If  such  a  condenser 
transmitter  be  connected  between  a  high 
potential  point  of  the  antenna   (e.  g., 
the  topmost  point  of  the  loading  coil, 
L  of  Figure  137)   and  ground,  it  will 
have  two  effects  when  its  capacity  is 
varied  by  the  sound  waves.     To  begin 
with,   it   will  detune   the  antenna  by 
shunting  the  coil  L  and  the  radio  frequency  alternator  A  by  a  larger 
or  smaller  capacity   (which  capacity  is,  in  effect,  in  parallel  with  the 
antenna  capacity).    This  effect  may  be  considerable  if  the  antenna  capa- 
city is  small,  the  antenna  damping  small,  and  condenser  transmitter 
capacity  variations  large.    Figure  138  depicts  the  curve  of  antenna  cur- 
rent (ordinates)  against  frequency  to  which  antenna  is  tuned  (abscissas) 
with  the  alternator  A  run  at  constant  frequency  corresponding  to  the 
point  A  on  the  curve  and  the  peak  of  the  resonance  curve.    The  proper 
point  to  work  the  antenna  for  such  a  system  would  be  at  some  such  point 
as  F  on  one  of  the  steeply  falling  branches  of  the  resonance  curve.    Then, 
if  the  frequency  were  altered  periodically  between  OB  and  OD  by  the 
condenser  transmitter,  the  antenna  current  would  similarly  vary  periodic- 
ally between  EB  and  DG.    The  second  effect  of  varying  the  capacity  of 
the  condenser  transmitter  would  be  actually  to  " spill"  energy  from  the 
antenna  to  ground  through  the  transmitter  capacity.     These  two  effects 
should  assist  each  other  and  the  reader  can  satisfy  himself  by  a  little 
thought  on  the  subject  that  this  result  can  be  secured  by  tuning  the 
antenna  system  with  the  condenser  transmitter  in  its  undisturbed  posi- 
tion to  a  lower  frequency  (that  is,  longer  wave  length)  than  that  of  the 
alternator.    If  the  opposite  is  done,  the  two  effects  of  the  condenser  may 
partially  or  entirely  neutralize  each  other. 

Continuing  our  consideration  of  high  current  microphones  for  modu- 
lation in  radio  telephony,  we  come  to  a  type  of  telephone  relay  used 
by  Mr.  W.  Dubilier.  The  radiophone  transmitter  with  which  it  is  em- 


142 


Dubilier  Line-to-Radio  Relay 


i 
i 


B    CD 

Frequency 


FIGURE    138 — Detuning    characteristic    of 
radiophone  transmitter. 

ployed  has  been  illustrated  in  Figures  37,  38,  and  39.  The  inventor  (in 
1911)  was  well  aware  of  the  advantage  of  transferring  speech  from  tele- 
phone lines  to  the  radiophone  transmitter  and  designed  the  relay  for  that 
purpose.  A  description  thereof  follows: 

' '  Figure  139  shows  a  cross  section  of  the  relay.    The  complete  trans- 
mitter consists  of  the  magnets  A,  A  wound  with  two-ohm  winding  B,  B, 


/s-i-  WATER  OUTLET 


WATER   INLET-*' 


FIGURE  139— Cross  section  of  Dubilier  high  current  telephone  relay. 


Berliner  Company  High  Current  Microphone 


143 


and  placed  opposite  to  each  other  with  the  diaphragms  and  carbon  con- 
taining cup  between.  (There  had  been  adopted  a  type  of  transmitter 
with  two  diaphragms  with  the  carbon  between,  both  diaphragms  swing- 
ing inward  or  outward  in  synchronism  and  thus  producing  greater 
changes  in  the  resistance  of  the  carbon  between  them  than  if  one  of 
them  were  fixed).  The  diaphragms  are  approximately  5  inches  (12.7  cm.) 

in  diameter  and  0.036  inch  (0.9  mm.)  thick. 
The  ebonite  disc  D  is  used  to  mount  the  dia- 
phragms, and  is  drilled  with  large-sized  holes 
so  as  to  prevent  'air  packing'  or  talking 
against  each  other. 


FIGURE  140 — Cross  section 

of    carbon-containing 

cup  of  Dubilier  high 

current  relay. 


' '  A  cross  section  of  the  carbon-containing 
cup  is  shown  in  Figure  140.  It  resembles  three 
brass  rings  placed  one  within  another,  forming 
three  independent  containing  portions.  Water 
circulates  through  the  chambers  F  and  H  by 
means  of  the  inlet  and  outlet  tubes  /,  and  the 
middle  chamber  G  (of  Figure  139)  is  used  to 
retain  the  carbon  granules.  To  make  contact 
with  the  granular  mass,  circular  rings  of 
platinum,  J,  J  are  used,  which  are  first  sol- 
dered to  the  diaphragms  Cf  C.  The  platinum 
rings  are  drilled  with  small  holes  round  the 
entire  circumference  so  as  to  allow  a  free  cir- 
culation of  air,  and  through  one  of  these 
holes  the  small  inlet  and  outlet  tubes  are  run. 
The  contact  is  made  in  the  center  of  the  granu- 
lar mass.  A  mica  disc  is  used  to  retain  the 
granules  in  the  chamber. ' ' 

The  transmitter  in  question  was  designed 
to  carry  currents  up  to  6  amperes.  It  seems 
to  have  been  operative ;  since,  as  stated  pre- 
viously, radio  telephony  over  250  miles  (400 
km.)  was  accomplished  with  such  apparatus. 
In  Figure  141  is  shown  in  detail  the  high 
current  microphone  transmitter  used  by  the 
Telephone  Manufacturing  Company  (for- 
merly J.  Berliner)  of  Vienna.  The  entire 
radiophone  set  of  which  it  is  a  part  was  illustrated  in  Figure  22.  The 
microphone  is  seen  to  be  mounted  on  a  frame  support  with  a  ratchet 
clutch  for  holding  it  at  any  desired  height.  On  the  front  of  its  case  are 
the  large  mouthpiece  and  a  double  throw  switch  for  "  Calling"  or  "  Speak- 


FIGTJRE  141 — Heavy  current 
Berliner  microphone  trans- 
mitter with  fan  cooling. 


144 


Egner-Holmstrom  Transmitter 


ing."    Directly  beneath  the  transmitter  is  placed  a  horizontal  fan  for 
cooling  purposes. 

In  building  high  current  transmitters,  the  granular  carbon — carbon 
diaphragm  type  (e.  g.,  as  built  by  the  Berliner  Company)  has  been 
found  to  be  suitable.  The  usual  modifications  made  therein  when  used 


FIGURE  142 — Front  view  of  Egner-Holmstrom  high  current 
transmitter. 


for  the  unusually  large  amounts  of  energy  necessary  in  radio  telephony 
are  to  replace  the  felt  packing  of  the  microphone  chamber  by  asbestos 
packing  or  packing  of  some  other  uninflammable  material,  and  to  per- 
forate the  metal  case  so  as  to  permit  air  cooling. 

One  of  the  most  remarkable  and  effective  of  high  current  microphones 
is  that  devised  by  Messrs.  C.  Egner  and  J.  G.  Holmstrom  of  Stockholm, 


Egner-Holmstrom  Transmitter 


145 


Sweden.  The  inventors  state  that  a  normal  microphone  which,  for  a 
current  of  a  few  milliamperes  has  a  resistance  of  say  200  ohms,  at  a 
current  of  1  ampere  has  a  resistance  of  only  5  to  8  ohms.  The  micro- 
phone is  shown  in  plan  in  Figure  142  and  in  actual  appearance  in  Figure 


FIGURE  143 — Egner-Holmstrom  high  current  microphone. 

143.  Corresponding  parts  are  indicated  by  the  same  lettering.  The 
whole  device  is  provided  with  oil  (or  other  fluid)  cooling,  by  the  attach- 
ment of  the  cooling  reservoir  H  (of  part  A  of  Figure  143)  to  the  back 
of  the  microphone  chamber.  Through  this  cooling  chamber  run  the  sup- 
porting arid  connecting  rods  from  each  of  the  microphones  A.  It  will 
be  noticed  from  Figure  142  and  part  B  of  Figure  143  that  there  are  16 
of  these  microphones,  which  can  be  connected  together  in  various  ways 
as  indicated  below.  The  rods  which  run  from  the  microphones  through 
the  cooling  reservoir  terminate  on  the  connecting  board  /  (part  C  of 
Figure  143).  The  cooling  fluid  is  arranged  to  circulate  in  a  fashion 
similar  to  the  "  thermo-syphon "  system  sometimes  used  for  gas  engines, 
and  heat  is  radiated  from  the  flanges  of  the  cooling  chamber  H.  The 
cooling  fluid  must  be  an  insulator. 

The  individual  microphones  are  connected  together  permanently  in 
8  sets  of  2  each,  the  2  being  always  adjacent  on  the  same  row.  The 
back  of  the  microphone  chamber  is,  in  each  case,  a  copper  plate  covered 
with  thin  carbon,  and  is  fixed.  From  the  copper  plates  pass  the  rods 
to  the  rear  connecting  board,  previously  mentioned.  The  vibrating 
electrodes  C  (of  Figure  142  and  part  B  of  Figure  143,)  are  4  in  number, 
each  taking  care  of  4  of  the  microphones  back  of  it.  These  microphones 
are  insulated  from  each  other  by  being  supported  on  cylinders  of  glass  B 


146  Egner-Holmstrom  Transmitter 

(part  B  of  Figure  143)  which  cylinders  are  in  turn  attached  to  the  main 
vibrating  diaphragm.  The  reason  for  the  use  of  glass  or  a  similar 
poor  conductor  of  heat  is  that  it  is  desired  to  prevent  overheating  of  the 
main  diaphragm  since  this  has  been  found  to  lead  to  speech  distortion. 
The  individual  microphone  chambers  are  made  up  of  rings  of  asbestos 
or  a  similar  heat-resistant  material,  pressed  by  spiral  springs  against  the 
electrodes  C  so  as  to  close  the  microphone  chambers. 

The  main  diaphragm  is  a  thin  sheet  (0.2  mm.  or  0.008  inch)  of 
aluminum  or  magnalium  which  is  stretched  as  tightly  as  possible.  The 
stretching  is  accomplished  by  tightening  up,  one  after  another,  the  screws 
F  (Figure  142  and  part  A  of  Figure  143).  Since  the  4  vibrating  elec- 
trodes C  are  attached  rigidly  to  the  central  portion  of  the  main  dia- 
phragm, they  will  vibrate  in  the  same  phase  and  amplitude.  It  is  this 
fact  which  renders  it  possible  to  secure  a  stable  arrangement  of  micro- 
phones in  parallel  in  the  Egner-Holmstrom  transmitter. 

In  order  to  increase  the  internal  resistance  and  resistance  variations 
of  the  transmitter,  hydrogen  or  some  hydrogen-containing  gas  is  passed 
through  the  microphone  chamber  by  means  of  the  inlet  and  outlet  pipes 
E.     Normally  the  gas  supply  required  is  practically  nil  after  the  air 
originally  present  in  the  microphone  chamber  has  been  displaced. 
'         The  various  ways  in  which  the 
individual  microphones  can  be  con- 
nected are  shown  in  Figure  144.  These   (T^\\ 
are  as  follows:  V*   «\^        J    6  J         I    c    1 

(a)  8    microphones    in    parallel, 
each  of  2  in  series.     Proper  applied 
voltage — 10-15    volts.      Proper    cur- 
rent— up  to  20  amperes. 

,,^A        •         i  •  n^i     FIGURE  144 — Connection  arrangements 

(b)  4    microphones    an    parallel,        Qf  Egner.Hoimstrom  high  current 

each  of  4  in  series.     Voltage — 20-30  microphone, 

volts.    Current — up  to  10  amperes. 

(c)  2  microphones  in  parallel,  each  of  8  in  series.    Voltage — 40-60 
volts.    Current — up  to  5  amperes. 

It  will  be  seen  that  the  microphones  can  handle  up  to  200  to  300 
watts  (12  to  18  watts  per  individual  microphone).  The  usual  current 
(corresponding  to  case  (b)  above)  is  10  amperes,  but  the  makers  of  the 
transmitter,  the  Aktiebolaget  Monofon  of  Stockholm,  are  prepared  to 
build  the  transmitters  to  carry  up  to  16  amperes  under  these  conditions 
There  are  about  0.3  cubic  centimeter  (0.018  cubic  inch)  of  carbon  granules 
in  each  individual  microphone. 

Messrs.  Bgner  and  Holmstrom  tried  out  their  transmitter  in  con- 


Marzi  Moving  Carbon  Microphone 


147 


nection  with  Professor  Poulsen's  apparatus  shown  in  Figure  13.  On 
June  29th  and  30th,  1909,  as  previously  stated,  clear  communication  was 
achieved  using  this  transmitter  with  6  amperes  in  the  antenna  between 
Lyngby  and  Esbjerg,  a  distance  of  170  miles  (270  km.). 

Another  form  of  microphone  transmitter  of  considerable  interest 
was  used  by  Mr.  R.  Goldschmidt  of  Laeken  (near  Brussels)  in  conjunc- 
tion with  the  apparatus  shown  in  Figure  67.  The  device  in  question  is 


FIGURE     145 — Scheldt-Boon    Marzi    high 

current  microphone  transmitter 

(relay  type). 

the  invention  of  Mr.  J.  B.  Marzi  of  Cornigliano  (Liguria,  Italy).  The 
basis  thereof  is  an  attempt  to  prevent  burning  of  the  carbon  grains 
when  heavy  currents  are  used  by  the  expedient  of  using  a  moving  stream 
of  carbon  grains.  Very  finely  powdered  carbon  will  flow"  in  practically 
the  same  manner  as  a  liquid  stream,  and  a  portion  of  the  carbon  stream, 
passing  between  two  electrodes,  is  used  in  this  case  as  the  microphone. 
The  actual  apparatus  is  shown  in  Figure  145,  and  the  cross  sections  of 
several  forms  thereof  and  the  mode  of  connection  are  given  by  Figure 
146.*  Referring  to  parts  I,  II,  and  III  of  the  latter  Figure,  a  reservoir 

*  Figures  145  and  146  are  reproduced  by  permission  from  the  French  journal  "T.S.F." 
and   based  on  material   from   Mr.    Scheidt-Boon   of  Brussels    (1914). 


148 


Marzi  Telephone  Relay 


5  is  filled  with  finely  powdered  carbon  and  from  this  reservoir  a  fine 
stream  of  carbon  flows  through  the  hollow  pipe  6  till  it  is  compelled  to 
pass  between  the  platinum  surfaces  9.  These  may  be  portions  of  con- 
centric spheres  (as  in  part  I),  or  an  obliquely  cut  cylinder  and  a  plane 


FIGURE  146  —  Details  of  Marzi  high  current  microphones  and  relays. 


surface  (as  in  part  II),  or  portions  of  two  coaxial  cones  (as  in  part  III). 
In  any  case  the  carbon  streams  between  these  surfaces,  which  are  the 
terminal  electrodes  of  the  high  current  microphone.  The  upper  one  of 
these  surfaces  is  usually  fixed  whereas  the  lower  one  is  movable,  either 
by  the  voice  directly  or,  as  shown  in  part  I,  by  means  of  an  armature  2 
controlled  by  the  electromagnets  1,  1.  The  current  for  these  electromag- 
nets is  derived  from  the  circuit  of  an  ordinary  telephone  transmitter,  or 
from  a  telephone  line.  It  is  this  feature  which  makes  the  device  a  relay. 
In  Figure  145  the  terminals  27  are  those  of  the  electromagnets  1,  1  and 
the  terminals  28  are  the  heavy  current  microphone  terminals. 

After  passing  the  surfaces  9,  9,  the  carbon  stream  flows  into  the  cup 
10.  At  regular  intervals,  the  contents  of  this  cup  should  be  emptied 
back  into  reservoir  5.  The  circuit  diagram  is  indicated  clearly  in  part 
IV  of  Figure  146.  As  will  be  seen,  the  ordinary  microphone  circuit  is 
coupled  through  the  induction  coil,  20,  21  to  the  circuit  containing  the 
electromagnets  1,  1  of  the  relay.  The  high  current  transmitter  is  shown 
placed  directly  "in  the  antenna,  though  it  can  equally  well  be  employed 


Chamber's  Liquid  Microphone 


149 


in  any  of  the  ways  shown  under  ordinary  "Microphone  Transmitter 
Control."  (page  133.)  The  weight  of  the  entire  apparatus  is  only  about 
9  pounds  (4  kg.)  and  the  height  thereof  18  inches  (45  cm.) .  As  previously 
stated,  this  transmitter,  carrying  3  amperes,  permitted  communication 
from  Laeken  to  Paris,  a  distance  of  200  miles  (320  km.). 


FIGURE  147 — Essential  parts  of  Chambers 
liquid  microphone. 

Another  method  of  attacking  the  problem  of  high  current  micro- 
phones has  been  the  attempt  to  use  conducting  liquid  jets  of  one  type 
or  another.  Figure  147  shows  the  essential  parts  of  a  simple  microphone 
of  this  sort  devised  by  Mr.  F.  J.  Chambers  in  1910.  At  A  a  stream  of 
electrolyte  under  a  head  of  about  3  feet  (1m.)  flows  past  the  needle 
valve  B.  Here  the  flow  is  adjusted  to  a  suitable  amount.  The  liquid 
then  passes  through  the  conducting  nozzle  C,  which  is  connected  to  F, 
one  of  the  terminals  of  the  microphone.  After  leaving  the  nozzle,  the 
liquid  stream  impinges  on  the  diaphragm  D  which  is  vibrated  by  the 
voice.  The  diaphragm  is  suitably  connected  to  E,  the  other  terminal 
of  the  microphone.  It  will  be  seen  that  the  up-and-down  motion  of  the 
diaphragm  will  alter  the  length  and  cross  sectional  area  of  the  jet  and 
consequently  its  resistance.  It  is  found  that  such  a  microphone,  because 
of  the  mechanical  damping  of  the  diaphragm  by  the  jet,  gives  clear 
articulation  without  rasping  noises.  The  distance  of  the  diaphragm 
from  the  nozzle  is  adjustable.  The  capacity  of  such  a  microphone  is 
limited  simply  by  the  necessity  of  preventing  the  current-carrying  electro- 
lyte from  boiling.  In  practice,  Mr.  Chambers  found  that  about  400 
watts  could  be  handled  by  such  a  microphone. 

Another  type  of  liquid  microphone,  somewhat  similar  to  that  of  Mr. 
Chambers,  has  been  devised  by  Professor  Giuseppi  Vanni  of  Rome. 
The  apparatus  is  shown  in  Figure  148.  A  centrifugal  pump  R,  made 
entirely  of  acid-resistant  materials  and  operated  by  a  small  motor, 
forces  a  jet  of  dilute  acid  out  of  the  ebonite  nozzle  T.  The  jet  then  falls 
on  the  inclined  surface  A,  is  deflected  to  the  oppositely  inclined  surface 
B,  is  again  deflected  and  then  passes  back  to  the  pump  to  resume  its 
circulation.  The  pump  pressure  corresponds  to  12  or  15  feet  (3  or  4  m.) 


150 


Vanni's  Liquid  Microphone 


of  water  column.  The  terminals  of  the  microphone,  H  and  P,  are  con- 
nected mechanically  to  the  electrodes  A  and  B.  B  is  fixed  but  A  is 
vibrated  back  and  forth  in  an  oblique  direction  practically  perpendicular 
to  the  deflected  jet.  Z  is  the  mouthpiece  of  the  microphone, 


FIGURE  148 — Vanni's  liquid  microphone. 

the  diaphragm  being  connected  at  0  to  the  mechanical  control  of  A. 
The  motions  of  A  not  only  change  the  cross  section  of  the  jet  from  a 
cylinder  to  a  flattened  sheet,  but  also  obstruct  the  stream  more  or  less 
by  the  greater  or  less  immersion  therein  of  A.  The  electrode  A  therefore 
acts  as  a  sort  of  shutter. 


FIGURE  149 — Vanni's  liquid  microphone 
relay. 


Majorana's  Liquid  Microphone 


151 


The  Vanni  microphone  has  also  been  arranged  as  a  relay  in  the 
fashion  illustrated  in  Figure  149.  The  usual  transmitter  H  supplies 
fluctuating  currents  to  the  electromagnets  E,  which  in  turn  control  the 
liquid  microphone  by  means  of  the  iron  diaphragm  NM.  This 
device  was  used  in  the  experiments  of  Professor  Vanni  previously 
described,  where  it  successfully  controlled  1  kilowatt,  permitting  radio 
telephony  625  miles  (1,000  km.).  These  experiments  were  described 
on  page  71. 

Another  principle  which  can  be  applied  in  liquid  microphones  is 
that  of  the  instability  of  liquid  jets,  as  first  discovered  by  Chichester  Bell 
in  1886.  The  phenomenon,  which  is  based  on  the  surface  tension  of  the 
liquid,  is  illustrated  in  Figure  150,  part  A.  This  shows  a  jet  of  liquid 
escaping  from  a  small  tube,  T.  The  orifice  of  the  tube  is  supposed  to  be 
smooth  and  circular.  The  jet  will  proceed  as  a  cylinder  for  a  certain 
distance,  and  then  a  slight  constriction  will  occur  at  the  point  A.  Directly 
below  A  the  stream  will  bulge,  and  then  constrict  still  more  below  the 
bulge.  At  B  the  stream  will  break  up  into  drops  which,  as  they  fall, 
will  vibrate  from  oblate  to  prolate  ellipsoids,  passing  through  the  spher- 
ical shape.  We  are  not,  however,  concerned  with  the  stream  after  it  has 
broken  up,  but  rather  with  its  cross  section  at  the  bulge  just  above  the 


FIGURE   150 — Essential  parts   of  Major- 
ana's  liquid  microphone. 

breaking-up  point.  For  it  is  found,  by  experiment,  that  the  transmission 
of  the  least  mechanical  disturbance  to  the  falling  jet  will  move  the  break- 
ing-up point  up  the  stream  toward  the  orifice,  and  the  motion  will  be 
quite  considerable  even  for  very  slight  mechanical  disturbances. 


152  Majorana's  Liquid  Microphone 

These  facts  have  been  utilized  by  Professor  Q.  Majorana  of  Rome  in 
his  hydraulic  microphone,  devised  in  1906.  Its  essential  parts  are  shown 
in  part  B  of  Figure  150.  The  tube  T  of  glass  or  other  insulator  has  a 
portion  of  its  wall  at  D  replaced  by  an  elastic  diaphragm  which  is  attached 
to  the  larger  voice-actuated  diaphragm  M  by  mechanical  means.  Placed 
in  the  jet  just  above  the  breaking-up  point  are  the  two  electrodes  8l  and 
S2  which  form  the  terminals  of  the  microphone.  It  is  clear  that  the  varia- 
tions of  cross  sections  of  the  jet  at  8^S2  will  cause  the  necessary  resistance 
variations.  One  unfortunate  drawback  with  this  form  of  liquid  micro- 
phone is  the  excessive  length  of  the  jet  (5  to  15  feet,  or  2  to  5  m.)  and 
its  very  great  sensitiveness  to  slight  shocks.  As  previously  described, 
Professor  Majorana  succeeded  in  telephoning  270  miles  (420  km.)  with 
such  a  microphone  control.  It  has  been  stated  that  the  device  can  control 
10  amperes  at  a  terminal  potential  difference  of  50  volts,  corresponding 
therefore  to  500  watts. 


CHAPTER  VII. 

(g)  VACUUM  TUBE  CONTROL  SYSTEMS;  GENERAL  METHODS; 
MEISSNER  RADIOPHONE;  CHARACTERISTIC  OF  TUBE  CONTAIN- 
ING GAS;  MARCONI  COMPANY  TRANSMITTER;  CIRCUITS  OF 
BOUND  ;  EXPERIMENTS  AND  TRANSMITTERS  OF  DE  FOREST  AND 
LOGWOOD  ;  TRANSMITTERS  OF  WESTERN  ELECTRIC  COMPANY  ; 
MODULATING  SYSTEM  OF  COLPITTS;  SYSTEM  OF  HEISING; 
TRANSMITTERS  OF  GENERAL  ELECTRIC  COMPANY;  MODULAT- 
ING SYSTEM  OF  WHITE  ;  HULL  PLIODYNATRON  TRANSMITTERS  ; 
COMPOSITE  ALEXANDERSON  ALTERNATOR  AND  PLIOTRON 
SYSTEMS;  TYPES  OF  ABSORPTION  MODULATION;  INFLUENCE 
OF  MODULATION  ON  SELECTIVITY. 

(g)  VACUUM   TUBE   CONTROL   SYSTEMS. 

As  has  been  previously  described  in  considerable  detail,  a  ready 
means  of  generating  moderate,  and  even  high  outputs  at  sustained  radio 
frequencies  is  by  the  use  of  the  various  types  of  hot  cathode  vacuum  tubes. 
These  tubes  depend  for  their  operation  as  oscillators  on  the  potential  of 
small  conducting  members  such  as  the  grid  in  audions,  oscillions,  and 
pliotrons.  Since  the  amount  of  energy  required  to  change  the  potential 
of  small-capacity  conducting  members  is  itself  minute,  it  would  seem 
a  priori  that  one  of  the  most  ready  means  of  modulating  the  output  of 
such  oscillators  would  be  by  altering  the  potential  of  the  member  in 
question  in  accordance  with  the  voice  vibrations.  As  a  matter  of  fact, 
the  proper  control  of  the  oscillations  generated  in  such  a  tube  is  not  a 
perfectly  simple  matter,  for  reasons  which  will  appear. 

There  are  at  least  two  available  methods  of  controlling  the  output 
of  vacuum  tube  oscillators,  and  instances  of  each  of  these  in  practice  will 
be  described.  The  first  of  these  is  by  variation  of  the  grid  potential, 
the  assumption  being  that  as  the  grid  potential  becomes  increasingly 
negative,  the  current  through  the  tube  (and  therefore  the  available 
radio  frequency  output)  continuously  and  proportionately  diminishes. 
Difficulties  of  stability  of  operation,  however,  arise  and  the  conclusion 
must  be  somewhat  modified.  The  second  of  these  methods  is  by  vary- 
ing the  plate  potential,  the  assumption  in  this  case  being  that  as  the 
plate  potential  becomes  increasingly  positive,  the  current  through  the 
tube  (and  therefore  the  available  radio  frequency  output)  continuously 

153 


154 


Meissner  Vacuum  Tube  Radiophone 


and  proportionately  increases.  This  conclusion  also  requires  some  modi- 
fication because  of  temperature  and  space  charge  limitation  of  plate 
current  and  because  of  the  limits  of  available  energy  which  must  thus 
be  introduced  into  the  plate  circuit.  (See  under  " Sustained  Wave 
Generators,"  part  (c),  "Vacuum  Tube  Oscillators;"  and  specifically  the 
descriptions  given  of  Figures  71,  72,  and  73,  page  77.) 


, 


FIGURE  151 — Telefunken  Company-Meissner 
radiophone  transmitter,  1913. 


There  ate  a  number  of  differences  between  the  operation  of  the  two 
systems  of  modulation  mentioned,  such  as  the  relation  between  the  modu- 
lated radio  frequency  energy  and  the  necessary  controlling  audio  fre- 
quency energy;  but  these  differences  will  best  be  brought  out  in  con- 
sidering the  actual  systems  in  use. 

Dr.  Alexander  Meissner  of  the  Telefunken  Company,  working  with 
the  tube  shown  in  Figure  83,  and  the  circuit  shown  in  Figure  81  for 
producing  the  oscillations,  succeeded  in  carrying  out  some  interesting 
experiments  in  radiophone  transmission.  He  states  that  using  a  plate 
circuit  voltage  of  440,  it  was  possible  to  obtain  a  radio  frequency  output 
of  12  watts  in  the  antenna.  This  corresponded  to  an  antenna  current  of 
1.3  amperes  with  an  antenna  resistance  of  7  ohms  at  a  wave-length  of  600 


Round  Control  System 


155 


meters.  No  statement  was  made  as  to  the  mode  of  control,  though  for 
such  small  powers  it  is  probable  that  a  heavy  current  microphone  would 
suffice  if  placed  directly  in  the  antenna  or  in  a  suitably  associated  circuit 
as  indicated  under  the  description  of  Figure  130,  page  133. 

The  radiophone  equipment  used  by  Dr.  Meissner  in  June,  1913,  for 
transmission  between  Berlin  and  Nauen,  a  distance  of  23  miles  (36  km.), 
is  shown  in  Figure  151.  The  von  Lieben-Reisz  bulb  is  mounted  at  the 
rear  of  the  apparatus  box. 

While  these  experiments  were  significant,  it  must  be  noted  that  Mr. 
H.  J.  Round  states  that  when  the  Lieben-Reisz  tubes  were  used  at  such 
outputs,  they  lasted  only  10  minutes  because  of  disintegration  of  the 
filament  by  the  positive  ionic  bombardment!  This  would  naturally 
render  their  use  under  such  conditions  impracticable  commercially. 


GrM 

Potential 


-I 

2 


PlabCurrtnt 


GrU/Cvr. 


FIGURE    152 — Plate-to-filament   and   grid-to- 
filament  characteristics  of  three  elec- 
trode hot  cathode  tube  con- 
taining gas. 

We  consider  next  the  radiophone  experiments  carried  out  by  Mr., 
Round  of  the  Marconi  Company.  To  begin  with,  we  shall  ,give  the  grid 
potential-plate  current  curves  found  for  his  tubes  by  Mr.  Round.  One 
of  these  is  shown  in  Figure  152.  It  should  be  carefully  compared  with 
that  shown  in  Figure  76  for  the  case  of  pure  electron  discharge  tubes. 
Mr.  Round's  description  of  Figure  152  (with  some  added  comments  and 
slight  alterations)  will  be  given:  "Suppose  the  plate  to  be  made  so 

positive  that  the  whole  tube  would  be  glowing  (i.  e.,  filled  with  blue 

. 

. 


156 


Marconi  Company  Bulb  Radiophone 


glow  of  the  usual  ionised  gas  discharge)  except  for  the  presence  of  the 
grid.  Then,  starting  with  the  grid  strongly  negative,  notwithstanding 
the  plate  being  highly  positive,  the  electrons  cannot  get  through  the  grid 
because  the  grid  is  nearest  to  them.  At  a  very  small  negative  value  of 
the  grid  potential,  a  few  electrons  can  get  through  the  grid  and  will  fall 
to  the  plate  and  the  number  that  will  get  through  will  rapidly  increase 
until  the  grid  is  at  zero  potential ;  the  current  to  the  plate  then  having  the 
value  it  would  if  the  grid  were  absent.  Afterwards,  as  the  grid  becomes 
positive,  the  current  will  decrease  because  the  grid  will  absorb  some 
electrons. ' ' 

The  detailed  wiring  of  a  Marconi  Company  radiophone  transmitter 
(the  receiving  set  of  which  is  described  on  page  216)  is 
given  in  Figure  153.  It  will  be  seen  that  oscillations  are  produced  by 


FIGURE  153 — Marconi  Company  radiophone  transmitter. 

coupling  the  grid  circuit  L'C  with  the  plate  circuit  L"C'  by  means  of  the 
inductive  coupling  L'  L".  The  grid  circuit  also  contains  the  30  volt  bat- 
tery Br  and  the  3,500  ohm  resistance  R',  which  latter  is  shunted  by  a 
suitable  by-pass  condenser  permitting  the  transfer  of  radio  frequency 
currents  but  preventing  excessive  direct  grid  current.  Similarly,  the 
plate  circuit  also  contains  the  resistance  Blf  R2,  Rs,  each  of  which  is  500 
ohms,  and  the  resistance  R±  of  10,000  ohms.  These  prevent  excessive 
plate  current,  "blue  glow,"  and  tube  breakdown.  In  series  with  these 
is  the  plate  battery  B  of  500  volts.  The  aggregate  of  resistances  and 


Marconi  Company  Bulb  Radiophone  157 

battery  is  shunted  by  the  capacity  C"  of  the  plate  oscillating  circuit.  The 
radio  frequency  energy  thus  produced  is  transferred  to  the  antenna  cir- 
cuit at  L!  by  an  inductive  coupling.  The  presence  of  oscillations  in  the 
antenna  is  indicated  by  glowing  of  the  test  lamp  TL  which  can  be  short- 
circuited  when  not  in  use.  The  microphone  M  is  directly  inserted  in  the 
antenna  circuit,  and  can  also  be  short-circuited  for  purposes  of  tuning. 
The  battery  B"  used  for  lighting  the  filament  is  an  ordinary  80  ampere- 
hour  storage  battery.  The  battery  B'  for  providing  500  volts  consists  of 
four  cases  of  dry  cells.  These  were  found  suitable  for  the  needs  of  the 
occasion  since  only  10  to  20  milliamperes  (0.010  to  0.020  ampere)  were 
required.  Thus  the  input  is  from  5  to  10  watts.  The  set  is  arranged  so 


FIGURE  154 — Marconi  Company  radiophone  set, 

that  it  can  also  be  used  for  telegraphy  by  manipulating  the  key  K  in  the 
grid  circuit.  The  change-over  switch  from  sending  to  receiving  is  simple 
and  is  so  arranged  that  it  can  be  controlled  from  a  distance  thus  per- 
mitting handling  the  set  from  any  part  of  a  ship,  e.  g.,  the  chart  room. 
Needless  to  say,  the  duplicate  transmitter  (microphone)  and  receiver 
could  also  be  placed  there.  The  set  delivers  0.6  amperes  in  the  antenna, 
and  is  guaranteed  for  communication  over  30  miles  (50  km.)  with  ship 
antennas  100  feet  (30  meters)  high  and  200  feet  (60  meters)  apart.  The 
set  can,  however,  be  pushed  to  give  1  ampere  in  the  antenna  with  an 
estimated  sea  range  of  100  miles  (160  km.).  As  a  matter  of  fact,  com- 
munication was  established  with  such  a  set  between  Aldene,  New  Jersey, 
at  the  station  of  the  Marconi  Company  and  a  station  in  Philadelphia, 


158 


Experiments  of  Round 


Pennsylvania,  a  distance  of  65  miles  overland  (105  km.).  The  Aldene 
antenna  was  supported  on  two  200-foot  (60  m.)  towers  450  feet  (145  m.) 
apart.  The  actual  appearance  of  the  set  is  given  by  Figure  154.  The 
large  generating  valve  is  shown  at  V  between  the  vertical  supports.  To 
its  right  is  placed  the  small  receiving  valve. 

It  is  stated  by  Mr.  Round  that  the  telegraphic  range  of  these  sets  is 
twice  the  radiophonic  range.  The  tuning  is  found  to  be  unusually  sharp, 
in  fact,  almost  uncomfortably  so.  It  was  also  found  somewhat  difficult 
to  start  these  tubes  rapidly  in  cold  weather.  Just  before  the  war,  work 
was  proceeding  with  such  equipment  in  the  direction  of  a  selective  call 
system,  but  this  had  to  be  suspended. 

Using  tubes  of  the  sort  described,  Mr.  Round  succeeded  in  getting  3 
amperes  in  the  antenna,  which  would  probably  correspond  to  about  50 


FIGURE  155 — Marconi  Company-Round  radiophone  transmitter  of  1914. 


watts  output.  The  input  was  about  0.100  ampere  at  2,000  volts  or  200 
watts,  thus  giving  an  efficiency  of  about  25  per  cent.  The  efficiency  here 
referred  to  is  the  so-called  ' '  electron  efficiency ' ' ;  that  is,  it  does  not  in- 
clude in  the  input  the  energy  required  for  lighting  the  filament,  but  con- 
siders only  the  plate  circuit  input  and  the  radio  frequency  output.  Mr. 
Round  considers  2,000  volts  to  be  excessively  high  for  tubes  of  this  sort, 
and  states  that  experiments  are  being  conducted  whereby  it  is  hoped  to 
make  the  tubes  available  for  use  at  lower  voltages.  The  serious  objection 
to  lower  voltages  is  that  the  high  supply  currents  then  required  for  ap- 
preciable outputs  produce  very  rapid  filament  disintegration  if  gas  be 
present. 


Logwood  Oscillion  Radiophone  159 

Another  form  of  the  Marconi  Company's  radiophone  transmitter  is 
shown  in  Figure  155.  Here  a  master  oscillator,  Vlt  is  used,  the  output  of 
which  passes  through  an  intermediate  circuit  T  to  the  grid  circuit  of  an 
amplifier,  V2.  The  output  of  amplifier  V2  is  transferred  to  the  antenna 
through  an  inductive  coupling.  The  modulation  control  in  this  system 
is  accomplished  by  placing  a  microphone  in  the  intermediate  circuit  thus 
varying  the  radio  frequency  voltage  impressed  on  the  amplifier  grid.  This 
system  of  master  oscillator  and  amplifier  is  of  considerable  interest  and 
the  illustration  shows  one  of  the  earliest  forms  thereof.  The  details  of  the 
master  oscillator,  Vlt  are  seen  to  be  those  of  Figure  153.  The  amplifier 
V2  is  very  similar  except  that  its  grid  and  plate  circuits  are  not  coupled. 
It  will  be  noted  that  both  the  master  oscillator  and  the  amplifier  are  fed 
from  the  same  plate  generator  G.  Here  we  have  a  case  where  the  micro- 
phone does  not  have  to  handle  the  Avhole  of  the  antenna  energy,  and 
indeed  the  amount  handled  by  the  microphone  M  is  roughly  the  antenna 
energy  divided  by  the  amplification  produced  in  V2.  A  modification  of 
this  system  omits  the  amplifier  but  uses  the  microphone  as  part  of  the 
coupling  between  L2  and  L3  in  the  master  oscillator,  thus  suitably  varying 
its  output. 

A  recent  type  of  Marconi  Company  sustained  wave  bulb  transmitter 
is  shown  in  Figure  156.  As  will  be  seen,  it  includes  two  bulbs,  each 
enclosed  in  a  ground-glass  front  compartment.  The  three  instruments  at 
the  top  of  the  case  indicate  the  plate  current,  antenna  current,  and  fila- 
ment current.  Means  for  regulating  the  filament  currents,  for  tuning 
the  various  circuits,  and  for  varying  the  regenerative  coupling  between 
the  grid  and  plate  circuits  are  provided. 

We  consider  next  the  oscillion  radiophone  transmitters  manufac- 
tured by  the  de  Forest  Radio  Telephone  and  Telegraph  Company.  One 
type  of  these  is  illustrated  diagrammatically  in  Figure  157,  and  this  ar- 
rangement of  circuits  is  due  to  Mr.  C.  V.  Logwood.  It  will  be  seen  that 
the.  direct  current  generator  G  (usually  of  1,200  to  1,500  volts)  is  con- 
nected in  series  with  the  iron  core  choke  coil  L'  and  shunted  by  the  con- 
denser C",  the  purpose  of  these  being  to  cut  down  the  "commutator 
ripple"  thus  giving  a  more  nearly  constant  e.  m.  f.  in  the  plate  circuit. 
Failure  to  observe  this  precaution  leads  to  a  loud  and  objectionable  hum 
corresponding  to  the  frequency  with  which  the  commutator  segments  pass 
under  the  generator  brushes.  The  oscillating  circuit  used  seems  to  be  of 
the  capacitive  coupling  type  or  ultraudion  type  according  to  the  method 
of  classification.  It  is  clear  that  the  antenna  capacity  is  used  as  a  portion 
of  the  oscillating  circuit  and  that  the  antenna  resistance  is  used  to  absorb 
the  output  of  the  bulb.  Modulation  is  accomplished  by  impressing  audio 
frequency  potential  variations,  produced  by  the  voice,  on  the  grid.  The 
microphone  M  causes  varying  currents  in  the  circuit  of  the  transformer 


160  Marconi  Company  Bulb  Radiophone 

primary  P,  whence  the  potential  variations  are  produced  by  the  secondary 
S  in  the  filament-to-grid  circuit.  The  resistance  R±  in  series  with  8  serves 
to  keep  the  grid  strongly  negative  because  of  the  difficulty  experienced 


FIGURE  156 — Marconi  Company  Sustained  Wave  Bulb  Transmitter. 

by  any  negative  charges  on  the  grid  in  leaking  off  to  the  filament.  By 
varying  R19  the  grid  potential  can  be  varied.  For  telegraphy,  the  key  K 
is  used.  It  merely  opens  the  grid  leak  circuit,  whereupon  the  grid  imme- 
diately becomes  so  negative  as  to  choke  off  all  plate  current  and  thus  stop 
the  oscillations  entirely.  Closing  the  key  permits  the  excess  negative 
charge  to  leak  off  the  grid  and  the  oscillations  start  again. 


de  Forest  Company  Oscillion  Radiophones 


161 


There  is  a  marked  tendency  to  increase  the  dimensions  ana  available 
output  of  the  tubes  employed,  and  this  is  well  illustrated  in  Figure  158. 
The  left  hand  tube  is  of  approximately  the  dimensions  of  the  usual  ampli- 
fier or  "repeater"  bulbs  used  by  the  Western  Electric  Company  in  trans- 
continental wire  telephony.  This  company  is  operating  under  exclusive 
patent  licenses  granted  fey  the  de  Forest  Company.  The  right  hand  bulb 
is  one  of  the  latest  0.25  kilowatt  input  oscillions.  A  3  or  4-inch  (7.5  or  10 
cm.)  "laboratory  oscillion"  is  shown  mounted  on  its  panel  in  Figure  159. 


VMWWAWVWAA/W 


FIGURE  157 — de  Forest  Company-Logwood  radiophone  transmitter. 

Such  a  device  can  produce  conveniently  a  number  of  watts  of  radio  fre- 
quency energy  of  constant  amplitude. 

A  whole  series  of  radiophone  transmitters  have  been  put  on  the  mar- 
ket by  "the  de  Forest  Company  some  of  which  are  here  illustrated.  A 
low  power  set  using  what  is  practically  one  of  the  tubular  receiving 
bulbs  is  seen  in  Figure  160.  A  larger  type  of  transmitter  and  receiver, 
together  with  the  requisite  motor  generator  set,  appears  in  Figure  161. 
This  set  is  stated  to  have  a  telegraphic  range  over  water  of  40  miles 
(64  km.)  using  masts  200  feet  (60  m.)  high  and  an  antenna  span  of  at 
least  250  feet  (80  m.).  The  generator  of  the  motor  generator  set  in  this 
case  is  for  1,000  volts  and  100  watts  output.  Though  detailed  wiring 
diagrams  of  the  arrangement  shown  in  Figure  161  are  not  available,  it 
is  of  some  interest.  It  shows  a  complete  de  Forest  radiophone  trans- 
mitter and  receiver.  At  the  left  is  shown  the  bulb-mounting  panel.  Dr. 
de  Forest  has  given  the  name  of  "oscillion"  to  the  bulb  shown  in  the 
figure.  This  bnlb  has  a  tungsten  "  W"  filament,  a  grid  of  tungsten  wire 


162 


de  Forest  Company  Oscillions 


wound  on  a  glass  support,  and  two  nickel  plates.  As  seen  from  the 
figure,  the  bulb  is  air-cooled  by  means  of  the  small  fan  placed  under- 
neath it.  The  two  instruments  mounted  on  top  of  the  panel  are  re- 
spectively indicators  of  the  filament  amperage  and  plate  circuit  current 
of  the  oscillion.  The  switch  at  the  left  hand  side  turns  the  plate  cur- 
rent of  the  tube  on  and  off.  The 

MBHHF  filament     current    control-rheostat 

handle  is  shown  in  the  lower  right 
T»  hand  corner  of  this  panel.    In  the 

middle  box  are  mounted  the  vari- 
ous portions  of  the  oscillating  cir- 
cuits and  microphone  control  ap- 
paratus. The  microphone  trans- 
mitter is  visible  on  the  front. 
The  equipment  to  the  right  of  the 
figure  is  a  fairly  normal  audion  re- 
ceiving set.  A  more  recent  set  of 
this  type  is  shown  in  Figure  163. 
The  small  ammeter  at  the  top  left 
indicates  the  filament  current  of 
the  bulb,  which  requires  somewhat 
careful  setting  for  full  output.  The 
right  hand  top  instrument  is  the 
antenna  ammeter.  A  convenient 
form  of  protected  change-over 
switch  from  sending  to  receiving  is 
mounted  on  the  back  of  the  panel, 
the  handle  projecting  just  to 
the  right  of  the  microphone  arm. 
The  bulb  is  also  mounted  back  of 
the  panel,  and  can  be  partly  viewed 
through  a  slit  under  the  microphone 
arm.  The  variable  condenser  to  the 
left  of  the  arm  is  condenser  C±  of 
Figure  157.  A  filament  rheostat  and' 
binding  posts  for  the  filament  bat- 
tery, antenna  and  ground  connec- 
tions, etc.,  completes  the  installation  except  for  a  short-circuiting  bar  be- 
tween two  binding  posts.  This  latter  may  be  removed  and  replaced  by 
the  Morse  key,  then  permitting  telegraphy. 

An  extremely  interesting  aeroplane  radiophone  transmitter  is  shown 
complete  in  Figure  164.  The  generator  is  driven  by  the  air  propeller 
with  suitable  speed  control  devices,  and  is  enclosed  in  the  "stream  line" 


FIGURE  158 — de  Forest  0.25  K.W.  os- 
cillion  (as  compared  with  type  of 
bulb  used  in  long  distance  wire 
telephony. ) 


de  Forest  Oscillion  Radiophones 


163 


FIGURE  159 — de  Forest  laboratory  oscillion 
transmitter. 


FIGURE      160 — de     Forest     low 
power  radiophone  transmitter 
(Type    PJ). 


casing,  the  terminal  leads  being  brought  out  of  the  rear  end.  The 
oscillion  is  mounted  in  a  protective  wire  mesh  casing  and  is  suspended 
in  such  fashion  as  to  be  reasonably  safe  from  breakage.  The  three  top 
instruments  are  for  antenna  current,  plate  circuit  current,  and  filament 
current.  The  Morse  key  is  shown  at  the  bottom  of  the  figure  together 


FIGURE  161 — de  Forest  "oscillion"  radiophone  transmitter  (and 

receiving  set). 

with  the  microphone.   The  latter  is  so  arranged  as  to  fit  closely  to  the  lips 
)f  the  user  and  thus  avoid  picking  up  the  extremely  loud  noise  of  the 
jine  exhaust. 
A  more  elaborate  type  of  radiophone  transmitter  using  three  oscillion 


164 


de  Forest  Oscillion  Radiophones 


bulbs  is  shown  in  Figure  165.  It  includes  a  "modulator"  or  master 
oscillator  bulb  and  two  * '  radio ' '  or  amplifier  bulbs.  These  are  mounted 
back  of  the  panel,  and  can  be  viewed  through  the  three  slits.  The  four 
instruments  at  the  top  of  the  board  (starting  at  the  left)  are  respectively 


FIGURE  162 — de  Forest  oscillion  radiophone  and  radio  tele- 
graph transmitter  and  receiver  (Type  OJ3). 

for  the  "modulator"  current,  plate  circuit  current,  filament  circuit  cur- 
rent, and  antenna  current.  The  inductance  and  variable  condenser  of  the 
master  oscillator  circuit  are  mounted  directly  below  the  corresponding 
ammeter  at  the  left.  An  antenna  loading  inductance  and  a  control  switch 
for  changing  from  receiving  to  transmitting  are  mounted  to  the  right  of 


FIGURE  163— de  Forest  0.25  K.W.  os- 
cilliou  radiophone  transmitter. 


de  Forest  Oscillion  Radiophones 


165 


the  microphone  transmitter.  Under  the  slit  of  each  bulb  are  its  filament 
and  plate  circuit  switches,  and  at  the  bottom  of  the  board  are  the  three 
filament  rheostats.  As  before,  two  binding  posts  are  provided  at  the 
bottom  of  the  board  for  the  insertion  of  a  Morse  key  if  radio  telegraphy 
is  desired.  A  set  of  this  type  is  supplied  with  1,500  volts  for  the  plate 
circuit  and  an  input  of  about  1.5  kilowatt.  The  telephone  range  over 
water  is  stated  to  be  400  miles  (640  km.)  and  the  corresponding  tele- 


FIGUBE  164 — de  Forest  0.25  K.W.  oscillion  radiophone  and  radio  telegraph 

transmitter. 

graphic  range  600  miles  (1,000  km.).    As  before,  towers  200  feet  (60  m.) 
high  and  250  feet  (80  m.)  apart  are  presupposed. 

Arrangements  were  made  by  the  de  Forest  Company  with  a  phono- 
graph company  whereby  almost  every  night  records  made  by  this  latter 
company  were  played  into  the  radiophone  transmitter  and  thus  rendered 
audible  to  a  wide  circle  of  listeners.  One  or  two  oscillions  are  used  in  the 
transmitter,  each  with  a  stated  output  of  0.25  k.w.  The  wave  length 
used  has  been  850  m.  This  service  was  given  about  five  nights  per 
week  beginning  October,  1916.  The  music  has  been  heard  a  number  of  times 
as  far  away  as  Buffalo,  New  York,  a  distance  of  306  miles  (490  km.)  and 
even  at  an  extreme  range  at  Mansfield,  Ohio,  a  distance  of  465  miles  (750 


166 


Experiments  of  de  Forest  Company 


km.).  One  interesting  result  of  this  work  has  been  a  "radio  dance" 
given  one  evening  at  Morristown,  New  Jersey,  a  distance  of  30  miles  (50 
km.)  from  the  de  Forest  station.  Music  was  transmitted  from  the  latter 
station  and  received  at  Morristown  on  a  receiving  set  with  a  three-step 
audion  amplifier.  The  resulting  "signals"  were  sufficiently  loud  to  per- 
mit the  dance  to  be  conducted.  Another  novel  field  for  radio  telephony, 
which  Dr.  de  Forest  believes  presents  great  promise,  is  that  of  news  dis- 
tribution in  rural  districts.  There  is  no  doubt  that  the  dissemination  of 


FIGURE  165— de  Forest  0.25  K.W.  3-oscillion  radio- 
phone transmitter. 


information  and  various  types  of  entertainment  in  districts  which  would 
otherwise  be  isolated  is  a  most  valuable  possibility  for  radio  telephony. 

As  is  well  known,  the  Western  Electric  Company  has  been  carrying 
on  extensive  research  work  in  radio  telephony  for  some  time  past.  (Some 
of  the  types  of  tubes  described  in  the  patents  of  that  Company  are  similar 
to  those  shown  in  Figure  95.  Generally  speaking,  platinum  filaments 
coated  with  metallic  oxids  are  there  indicated.)  A  method  of  modulation 
of  the  output  of  such  an  oscillator  has  been  developed  by  Mr.  E.  H. 
Colpitts.  It  is  depicted  in  Figure  166.  As  will  be  seen,  the  plate  oscillat- 
ing circuit  C1L1LI2C2  is  coupled  inductively  to  the  grid  circuit  CL  at  1^. 
It  is  also  coupled  inductively  to  the  output  circuit  L"C"  at  L2.  A  second 


Modulation  System  of  Colpitts 


167 


grid  circuit  is  also  provided  consisting  of  the  secondary  S  of  the  audio 
frequency  transformer  (the  primary  of  which  contains  the  microphone 
and  battery  5),  and  the  battery  Bl  for  maintaining  the  grid  at  a  nega- 
tive potential.  This  system  of  modulation  has  the  advantage  of  simplicity. 
On  the  other  hand,  it  may  easily  become  an  unstable  control  system.  The 
reason  for  this  is  the  following :  In  any  oscillating  tube,  the  amplitude  of 
the  plate  circuit  oscillations  increases  until  the  losses  in  the  tube,  and  in 
the  external  or  output  circuits  which  it  feeds,  utilise  the  entire  available 
energy.  The  amplitude  then  remains  constant.  It  is  evident  that  if  we 
make  the  grid  potential  extremely  negative,  so  that  the  plate  circuit 
oscillations  cannot  build  up  to  this  stable  value  just  mentioned,  the  oscilla- 


FIGURE  166 — Western  Electric  Company-Colpitts  modulation  system,  1914. 

tions  will  simply  cease  entirely.  Just  above  this  extremely  negative  grid 
potential,  there  is  a  narrow  range  of  grid  voltages  for  which  the  plate 
circuit  output  depends  on  the  grid  potential,  though  only  as  a  transient 
phenomenon.  A  static  characteristic  of  such  a  relation  between  grid  po- 
tential and  oscillating  current  in  the  plate  circuit  is  not  obtainable 
•because  the  effects  do  not  persist.  The  oscillating  current  tends  to  rise 
either  to  its  full  and  stable  amplitude  or  to  cease  altogether.  For  audio 
frequency  variations  of  moderate  magnitude  and  sufficient  rapidity  of  the 
grid  potential  the  system  is  sometimes  workable  though  always  with  the 
danger  just  mentioned  for  low  tones  or  for  extremely  loud  sounds. 

A  second  system  due  to  Mr.  Heising*  of  the  same  company  is  free 
from  the  objections  mentioned  in  that  the  tube  is  used  as  an  amplifier 
and  not  as  an  oscillator.  The  method  in  question  is  shown  in  Figure  167. 
The  radio  frequency  source  A  impresses,  through  the  transformer  P^S^ 
corresponding  radio  frequency  potential  variations  on  the  grid  Gl  of  the 
tube.  There  will,  therefore,  be  produced  in  the  output  plate  circuit  of 
this  tube  radio  frequency  current  variations.  Hence  there  is  an  available 


*Patent  1,199,180. 


168 


Modulation  System  of  Heising 


output  in  the  inductance  L,2.  The  tube  has  a  second  grid,  G2,  and,  as  will 
be  readily  seen,  there  are  impressed  on  G2  potential  variations  correspond- 
ing to  the  speech  amplitudes,  these  variations  being  produced  in  the 
customary  way  by  a  microphone  circuit  and  a  suitable  transformer.  The 
source  A  may  naturally  be  a  vacuum  tube  oscillator.  Each  grid  is  main- 
tained at  a  suitable  negative  potential  by  the  battery  B^  or  B2. 

A  series  of  long  distance  radiophone  experiments  were  carried  on  by 
the  Western  Electric  Company  from  the  United  States  Naval  Radio  Sta- 
tion at  Arlington,  Virginia.  This  station  has  an  antenna  600  feet  (180 
meters)  high.  Speech  was  transmitted  by  night  from  Arlington  to  the 
Eiffel  Tower,  Paris  (a  distance  of  3,900  miles  or  6,200  km.  almost  entirely 
over  water),  from  Arlington  to  Mare  Island,  California  (a  distance  of 
2,400  miles  or  3,800  km.  overland),  and  from  Arlington  to  Hawaii  (a 


FIGURE  167 — Western  Electric  Company-Heising  modulation  control 

system,  1915. 


distance  of  5,100  miles  or  8,300  km.,  about  half  over  water).  While  the 
transmission  could  be  achieved  only  under  exceptional  conditions  and  was 
in  no  sense  commercial,  it  is  of  marked  interest  in  indicating  how  great  a 
distance  can  be  bridged  by  even  a  very  moderate  amount  of  power  under 
favorable  circumstances.  One  is  reminded  of  the  feat  of  Sayville,  Long 
Island,  in  communicating  with  Nauen,  Germany,  a  distance  of  4,200 
miles  (6,700  km.)  with  only  6  kilowatts  in  the  antenna. 

The  apparatus  used  at  Arlington  wras  constituted  as  follows :  A  small 
bulb  (3  inches  or  7.5  cm.  in  diameter)  was  used  as  a  master  oscillator. 
The  filament  was  heated  from  storage  batteries  as  usual,  and  the  plate 
circuit  was  fed  from  125  volts  in  dry  batteries.  The  master  oscillator  had 
a  fairly  fine  grid.  Its  output  circuit  was  coupled  loosely  to  the  grid 
circuit  of  a  7-inch  (17.7  cm.)  " modulator"  bulb  with  a  coarser  grid. 
Comprised  in  this  grid  circuit  were  a  150  volt  battery,  to  give  the  grid 


Experiments  of  Western  Electric  Company 


169 


the  requisite  negative  potential,  and  the  secondary  of  a  150-to-l  air  core 
transformer  in  the  primary  of  -which  was  a  button-type  microphone  and 
its  supply  battery.  In  this  way,  the  voice  potential  variations  were  im- 
pressed on  the  modulator  grid  as  well  as  the  radio  frequency  variations. 
The  plate  circuit  of  the  modulator  was  tuned,  and  included  a  450-volt 
direct  current  generator. 

The  output  circuit  of  the  modulator  supplied  speech-modulated, 
radio  frequency,  potential  variations  to  the  fairly  coarse  grids  of  7-inch 
(17.7  cm.)  bulbs  all  connected  in  parallel.  Their  tuned  output  circuit  in 


mmmmmmmmmm 


FIGURE    168 — General    Electric    Company- 
White  method  of  producing  practical- 
ly constant  potential  from  A.  C. 


turn  fed  the  coarse  grids  of  from  300  to  over  500  "power"  bulbs  in 
parallel.  As  before,  these  grids  were  kept  at  a  constant  negative  potential 
of  — 150  relative  to  their  filaments.  The  plate  circuit  of  the  "power" 
bulbs  was  fed  from  a  large  600-volt,  direct  current  generator  which  was 
normally  used  for  the  Poulsen  arc  at  Arlington.  A  few  turns  of  heavy 
copper  band  in  this  last  plate  circuit  were  inductively  coupled  to  the 
tuned  antenna.  About  60  amperes  at  6,000  meters  wave-length  were 
normally  produced  in  the  antenna,  this  corresponding  to  something  over 
9  kilowatts.  The  efficiency  of  the  set  was  about  20  per  cent.  In  running 
the  set,  fairly  frequent  bulb  renewals  -  were  required,  thus  rendering  a 
high  upkeep  cost  of  operation  inevitable  (according  to  one  statement, 
$10,000  per  month). 


170 


White's  High  Voltage  D.  C.  Source 


The  apparatus  used  was  mounted  on  a  series  of  panels.  The  lower 
section  of  each  panel  had  the  necessary  switches  for  controlling  the  fila- 
ment and  plate  circuits  of  that  section.  The  upper  portion  of  each  panel 
was  in  two  halves.  On  each  half  were  mounted  25  of  the  7-inch  (17.7 
cm.)  " power"  bulbs,  all  cooled  by  air  brought  in  ducts  from  a  powerful 
blower.  The  cooling  ducts  were  at  the  rear  of  the  panel.  All  the  bulbs 
on  each  panel  portion  were  in  parallel.  Each  bulb  was  provided  with 
"Ediswan"  socket  base  so  as  to  be  readily  replaceable,  i.  e.,  all  terminals 
were  brought  out  through  this  base.  The  control  and  modulator  bulbs 
were  mounted  on  separate  small  panels. 

We  consider  next  a  number  of  radiophone  pliotron  transmitters  de- 
signed by  the  Research  Laboratory  and  especially  Mr.  William  C.  White 
of  the  General  Electric  Company.  The  mode  of  producing  reasonably 
constant  sources  of  high  potential  (from  alternating  current  supply)  will 
be  first  considered. 

The  method  referred  to  is  illustrated  in  Figure  168.  The  alternator 
A  sends  current  through  the  primary  P  of  a  transformer.  This  trans- 


FIGURE  169 — General  Electric  Company-White  radiophone  transmitter  for  al- 
ternating current  supply. 

former  has  two  secondaries.  Of  these  one,  S2,  is  arranged  to  light  the 
filaments  Fl  and  F»  of  two  kenotron  rectifiers.  There  are  comparatively 
few  turns  in  the  secondary  S2  because  the  filament  voltage  is  low.  A 
second  secondary  81  is  of  many  turns  so  as  to  furnish  a  high  voltage  to 
the  plates  Pl  and  P2  of  the  kenotrons.  It  will  be  noted  that  there  is  a 
central  tap  of  the  filament-feeding  secondary  82  the  purpose  of  which  is 
explained  in  connection  with  the  description  of  Figure  74.  It  prevents 


General  Electric  Company  Pliotron  Radiophones 


171 


injuriously  excessive  addition  of  the  filament-heating  and  thermionic  cur- 
rents in  either  end  of  the  filament.  The  middle  point  of  the  secondary  St 
is  connected  to  one  side  of  a  large  high  voltage  condenser  C  (e.  g.,  of 
several  microfarads),  the  other  side  of  which  condenser  is  connected  to 
the  middle  point  tap  of  the  filament-heating  secondary  /§f0.  It  will  be  seen 
that  the  condenser  will  be  charged  during  one-half  of  the  cycle  by  the 
left  hand  half  of  $t  in  series  with  kenotron  K l  and  during  the  other  half 
of  the  cycle  by  the  right  hand  half  of  81  and  the  right  hand  kenotron  7f  „. 
If  the  current  drawn  from  the  charged  condenser  is  comparatively  small 
(which  will  be  the  case  if  the  condenser  is  very  large  and  a  small  current 
at  high  voltage  is  drawn  therefrom),  the  potential  difference  at  its 
terminals  will  remain  appreciably  constant.  Experience  shows  indeed 
that  this  is  the  case,  and  it  has  proven  possible  to  get  so  nearly  constant 
a  potential  from  an  alternating  current  supply  in  this  way  that,  when 
used  in  the  plate  circuit  of  a  normal  pliotron  oscillator,  the  usual  a.  c. 
hum  has  been  practically  absent.  The  output  is  drawn  from  the  condenser 
terminals,  X,  Y. 


FIGURE  170 — General  Electric  Company-White  multiple  transformer  for 
feeding  plate  rectifier  and  filaments. 

Two  of  the  earlier  types  of  radiophone  transmitters  based  on  this 
principle  will  be  next  described,  the  description  being  due  to  Dr.  Irving 
Langmuir  of  the  General  Electric  Company.* 

' '  The  first  outfit  has  a  capacity  of  about  20  watts  in  the  antenna,  the 
source  of  power  being  the  local  city  supply,  which  is  118-volt,  60-cycle 
current.  This  is  connected  with  the  primary  of  a  small  transformer 
having  two  secondary  windings.  One  of  the  secondaries  is  designed  to 


*  "Proceedings   of   the 
1915. 


Institute   of   Radio   Engineers,"  Volume  3,  number  3,  September, 


172 


General  Electric  Company  Pliotron  Radiophones 


give  about  5  volts  and  furnishes  the  currents  used  for  heating  the  fila- 
ments of  the  kenotrons  and  pliotrons.  The  other  secondary  of  the  trans- 
former is  wound  to  furnish  a  potential  of  about  800  volts.  This  is  recti- 
fied by  means  of  a  kenotron,  and  serves  to  charge  a  condenser  of  about  6 
microfarads.  In  this  way,  a  source  of  high  voltage,  direct  current  is 
obtained  in  a  very  simple  manner.  The  plate  of  the  pliotron  oscillator 
is  then  connected  to  one  of  the  terminals  of  the  condenser,  while  the 
filament  is  connected  to  the  other.  The  plate  of  the  second  pliotron  is 
connected  to  the  grid  of  the  first,  while  the  grid  of  the  second  is  coupled 
by  means  of  a  second  small  transformer  to  the  microphone  circuit.  With 
this  small  outfit,  both  pliotrons  may  be  relatively  small.  .  .  . 

"In  the  second  outfit,  which  is  suitable  for  use  up  to  500  watts  or 


FIGURE  171 — General  Electric  Company-White  radiophone  transmitter 
for  direct  current  supply. 

more,  the  high  voltage  direct  current  is  obtained  from  a  small  2,000-cycle 
generator.  The  current  from  this  is  transformed  up  to  about  5,000  volts, 
rectified  by  kenotrons,  and  smoothed  out  by  means  of  condensers.  By 
the  use  of  2,000-cycle  alternating  current  instead  of  60-cycle,  it  is 
possible  to  store  up  large  quantities  of  energy  at  a  given  voltage  and  with 
a  permissible  fluctuation  of  voltage,  and  thus  obtain  as  much  as  a  kilowatt 
or  more  of  power  in  the  form  of  direct  current  with  condensers  of  mod- 
erate size.  This  high  voltage  direct  current  is  used,  as  before,  to  operate 


General  Electric  Company  Pliotron  Radiophones  173 

a  pliotron  oscillator,  the  output  of  which  is  controlled  by  means  of  a 
email  pliotron  connected  to  the  telephone  transmitter.  ...  "  Wire- 
line-to-radio telephone  transfer  has  been  accomplished  with  such  sets. 

Another  form  of  radiophone  transmitter  of  the  General  Electric 
Company,  described  in  Mr.  W.  C.  White's  patent  1,195,632,  is  shown  in 
Figure  169.  It  will  be  seen  that  the  grid  of  pliotron  amplifier  T1  is  con- 
nected to  the  filament  through  the  secondary  8  of  a  transformer,  the 
primary  of  which  contains  a  microphone  and  battery.  The  plate  circuit 
is  fed  at  X^Y^  by  exactly  the  same  form  of  device  as  shown  at  XY  in 
Figure  168.  For  the  sake  of  simplicity,  this  device  is  not  here  repeated 
in  the  diagram.  The  output  of  pliotron  T^  is  fed  into  the  plate  circuit  of 
pliotron  T,2  through  the  audio  frequency  transformer  P'S'.  The  second- 
ary of  this  transformer  is  shunted  by  the  condenser  Cj  which  acts  as  a 
practically  perfect  by-pass  for  the  radio  frequency  currents  in  the  plate 
circuit  of  T2  without  passing  any  appreciable  quantity  of  audio  fre- 
quency current  from  $'.  It  will  be  seen  that  the  tube  T2  is  an  oscillator 
since  its  grid  and  plate  circuits  are  coupled  through  the  antenna  circuit 
at  L  L'  and  LJL2.  Obviously,  the  method  of  modulation  control  here 
shown  is  an  extremely  stable  one.  It  consists  in  varying  the  plate  poten- 
tial of  oscillator  T2  in  accordance  with  the  speech.  This  implies,  however, 
the  injection  of  considerable  energy  into  the  plate  circuit  of  T,2  inter- 
mittently and  hence  the  necessity  for  amplifier  2\. 

For  use  with  a  radiophone  outfit  of  this  sort,  a  special  transformer 
shown  in  Figure  170  may  be  used.  This  has  the  single  primary  P  but  a 
number  of  secondaries  which  supply  the  following  circuits  (starting  from 
the  left)  :  filaments  of  the  oscillator  T29  filaments  of  the  kenotrons  which 
feed  the  amplifier  T19  plate  circuits  of  the  kenotrons  feeding  the  amplifier 
Tj.  and  the  oscillator  T,2  (at  different  voltages,  and  the  greater  for  the 
oscillator),  filaments  of  the  kenotrons  feeding  the  oscillator  T2,  and  fila- 
ments of  the  amplifier  2\.  Thus  the  entire  set  is  started  by  closing  one 
primary  circuit,  an  obvious  advantage. 

A  radiophone  transmitter  for  direct  connection  to  125  volt  direct 
current  circuits  is  shown  in  Figure  171.  The  plug  at  the  left  of  the  set  is 
merely  inserted  (with  correct  polarity)  into  a  lamp  socket  and  the  change- 
over switch  thrown  to  "transmit"  in  order  to  start  everything  in  the 
set.  It  will  be  seen  that  the  set  is  self-contained.  The  usual  microphone 
transmitter,  which  can  be  a  distance  from  the  remainder  of  the  set,  is 
seen  on  the  top  of  the  box.  Only  direct  current  (obtained  by  bridging 
the  microphone  across  a  portion  of  a  125-volt  potentiometer)  passes 
through  the  microphone.  At  the  top  of  the  box  at  the  left  is  mounted  a 
small  fixed  condenser  which  is  placed  across  the  feeding  line  to  reduce 
commutator  ripple  and  to  act  as  a  radio  frequency  shunt  in  the  plate 
circuit.  Thus  the  125-volt  current  feeds  the  plate  circuit  of  the  pliotron 


174 


General  Electric  Company  Pliotron  Radiophones 


which  is  mounted  inside  the  various  coils.  The  filament  is  lit  from  the 
125-volt  circuit  through  an  appropriate  resistance.  These  various  re- 
sistances and  potentiometer  are  shown  in  the  foreground  at  the  bottom 
of  the  box.  The  two  left  hand  coils  are  the  grid  circuit  coupling  to  the 
antenna  and  the  coils  at  the  right  the  plate  circuit  coupling,  a  circuit 


FIGURE  172 — General  Electric  Company-White  radiophone  transmitter 
for  alternating  current  supply. 


somewhat  like  that  in  Figure  169  being -used.  The  entire  set  weighs 
only  54  pounds  (20  kg.)  complete.  Completely  satisfactory  operation 
over  10  miles  (16  km.)  is  possible,  and  laboratory  tests  have  given  ranges 
up  to  65  miles  (105  km.). 

A  more  powerful  set  for  use  with  60  cycle  alternating  current  supply 
is  shown  in  Figure  172.    The  wiring  of  this  set  is  almost  identical  with 


Hull's  Pliodynatron  Modulation  Control 


175 


that  shown  in  Figures  168,  169,  and  170.  The  two  pliotrons  are  mounted 
at  the  top  of  the  box.  To  the  left,  under  them,  are  the  microphone  dry 
batteries.  To  the  right,  under  them,  are  the  "smoothing  condensers" 
(two  sets)  for  the  high  voltage  supply  in  the  plate  circuits.  To  the  bottom 
left  are  mounted  the  radio  frequency  coupling  coils  and  to  the  right  the 
four  kenotron  rectifiers.  The  panel  in  the  middle  carries  various  filament 
resistances,  and  back  thereof  are  mounted  the  microphone  transformer 
(PS  of  Figure  169)  and  the  amplifier  transformer  (P'S'  of  the  same 
figure).  The  entire  set  weighs  150  pounds  (68  km.).  The  transmitting 
range  for  satisfactory  service  is  50  miles  (80  km.). 

We  consider  next  the  control  systems  suitable  for  use  with  the 
dy natron  and  pliodynatron  tubes  of  the  General  Electric  Company  as 
developed  by  Dr.  Albert  W.  Hull.  A  description  of  the  dynatron  (and 


FIGURE  173— Effect  of  longitudinal  magnetic  field  on 
electron  paths  in  dynatron. 


pliodynatron)  together  with  their  mode  of  operation  is  given  in  con- 
nection with  Figures  96  through  101,  page  100,  and  the  reader  is  referred 
to  this  material  as  an  introduction  to  the  present  discussion. 

Figure  173  represents  the  cross  section  of  a  dynatron  where  F  is  the 
filament,  A  the  wires,  or  solid  portions,  of  the  anode,  and  P  the  plate. 
The  paths  of  a  few  electrons  away  from  the  filament  and  a  diagrammatic 
representation  of  a  few  of  the  electrons  leaving  the  plate  by  secondary 
emission  are  given  for  normal  conditions  in  the  left  hand  portion  of  the 
diagram.  The  effect  on  the  electron  paths  of  a  longitudinal  magnetic 
field  (parallel  to  the  filament)  is  shown  in  the  right  hand  portion  of  the 
figure.  It  will  be  seen  that  the  electrons  now  pursue  spiral  paths  and 
strike  the  anode  very  obliquely,  particularly  if  the  magnetic  field  is  very 
powerful  and  the  electron  velocity  small.  In  consequence,  comparatively 
few  will  get  through  the  anode  with  a  high  velocity,  and  therefore  the 
re-emission  phenomena  from  the  plate  will  be  much  diminished.  The 
characteristics  of  the  dynatron  will  be  progressively  altered,  as  indicated 


176 


Modulation  Characteristics  of  Pliodynatron 


in  Figure  174,  whence  the  magnetic  field  is  increased.  The  dotted  curve, 
A,  is  the  normal  dynatron  potential-current  curve.  On  applying  a  mod- 
erate magnetic  field  the  dashed  curve,  E,  is  obtained.  This  shows  no 
current  reversal  since  the  secondary  emission  is  already  small.  With  a 
strong  magnetic  field,  the  characteristic  becomes  the  full  line  curve, 
C,  and  shows  very  little  of  the  usual  dynatron  effect.  It  is  therefore  pos- 


\ 


FIGURE  174 — Characteristics  of  dynatron  in 
various  magnetic  fields. 


sible  to  control  the  negative  resistance  (and  hence  the  output)  of  a  dyna- 
tron by  the  superposed  magnetic  field,  and  this  field  may  be  that  due  to 
the  current  from  a  microphone  transmitter  passing  through  a  coil  suitably 
mounted  relative  to  the  tube. 

The  method  of  controlling  the  output  of  a  pliodynatron  would 
naturally  be  by  varying  the  potential  of  the  grid.  Offhand  it  might 
seem  that  this  would  either  stop  all  oscillations  (if  the  grid  were  suf- 
ficiently negative)  or  else  let  them  remain  at  full  intensity.  As  a  matter 
of  fact,  because  of  the  curvature  of  the  dynatron  characteristic  under 
certain  conditions,  it  is  possible  to  get  a  control  curve  of  the  pliodynatron 
(grid  potential-plate  current)  similar  to  that  shown  in  Figure  175.  This 
curve  has  a  considerable  straight  line  portion,  and  consequently  between 
A  and  B  thereon,  it  becomes  possible  to  control  the  output  of  the  tube 
by  varying  the  grid  potential.  The  actual  arrangement  is  shown  in 


General  Electric  Company  Pliodynatron  Radiophone          177 

Figure  176.    As  will  be  seen,  the  circuit  L^C^  is  connected  in  the  usual 
fashion  for  dynatrons  between  the  plate  and  the  battery  tap  point  J>. 

The  potential  variations  correspond- 
ing to  the  speech  are  placed  on  the 
grid  by  the  secondary  8  of  the  audio 
frequency  microphone  circuit  trans- 
former. The  modulated  output  passes 
to  the  antenna  circuit  through  the  in- 
ductive or  other  coupling  at  L.  In 
practice,  radio  telephony  over  a  dis- 
tance of  16  miles  (26  km.)  was  easily 
accomplished  with  one  pliodynatron ; 
but  this  range  could  doubtless  be 
much  increased  since  no  attempt  was 
made  at  the  time  to  get  the  greatest 
possible  output  or  range. 

A  system  of  radio  telephonic 
control  involving  both  an  Alexander- 
son  alternator  for  the  direct  genera- 


Amperes 


FIGURE  175 — Grid  potential-plate  cur- 
rent characteristic  of  a 
pliodyuatrou. 


tion  of  the  radio  frequency  energy  and  one  or  more  pliotrons  for  the 
modulation  and  control  thereof  is  shown  in  Figure  177.  As  will  be  seen, 
the  radio  frequency  alternator  is  coupled  inductively  to  the  antenna  by 
the  coils  2^  and  L2.  The  antenna  is  tuned  by  the  variable  inductance  L, 


FIGURE  176 — General  Electric  Company-Hull  pliodynatron  radiophone 

transmitter. 

and  the  top  H  of  the  tuning  inductance  is  the  point  of  highest  potential 
within  the  station  building.  (Of  course,  the  highest  potential  produced 
by  the  set  is  at  the  relatively  inaccessible  top  of  the  antenna.)  The  fila- 
ment of  a  large  pliotron  is  connected  to  the  ground,  and  the  plate  of 


178 


Pliotron  Absorption  Modulation  Control 


the  pliotron  to  the  point  H  at  the  top  of  the  tuning  inductance.  If  the 
filament  is  heated  by  alternating  current,  the  mid-point  of  the  step-down 
transformer  secondary  whereby  this  is  accomplished  is  connected  to 
ground  thus  equalising  the  thermionic  current  in  all  parts  of  the  fila- 
ment as  much  as  possible  (as  indicated  in  the  description  of  Figures  74 
and  75,  page  80).  If  the  grid  of  the  pliotron  is  kept  at  a  very  negative 
potential,  the  effect  on  the  antenna  energy  will  be  practically  nothing. 
As  the  grid  becomes  less  negative,  the  pliotron  permits  increasingly 
more  radio  frequency  current  to  pass  through  in  rectified  half  cycles, 


FIGURE  177 — General  Electric  Company- Alexanderson-White  alternator- 
pliotron  radiophone  transmitter. 

thus  withdrawing  energy  from  the  antenna.  In  other  words,  the  output 
of  the  alternator  either  passes  into  the  antenna  system  or  into  the  pliotron 
bulb.  It  is  found  by  experience  that  the  fact  that  the  pliotron  absorp- 
tion takes  place  only  for  half  cycles  does  not  affect  this  conclusion. 

It  will  be  noted  that  the  grid  is  normally  maintained  at  a  negative 
potential  by  the  battery  B^,  which  battery  is  shunted  by  the  condenser 
C  which  acts  as  an  audio  frequency  by-pass.  The  secondary  of  the  audio 
frequency  transformer  8  is  also  included  in  the  grid  circuit,  and  thus 
the  grid  potential  is  also  caused  to  vary  in  accordance  with  the  speech 
forms.  In  thus  controlling  the  antenna  energy  by  the  pliotron,  a  curious 
difficulty  arises.  The  impressed  radio  frequency  plate  potentials  are 
quite  high,  and  there  is  capacitive  coupling  between  the  plate  and  grid 


Effect  of  Internal  Bulb  Coupling 


179 


within  the  bulb  since  these  metallic  masses  are,  in  effect,  the  parallel 
plates  of  a  condenser.  In  consequence,  there  will  be  induced  smaller, 
though  still  troublesome,  radio  frequency  potential  variations  on  the 
grid.  During  the  positive  half  cycle,  a  positive  potential  is  induced  on 
the  grid  which  may  be  much  larger  than  the  potential  supplied  to  the 
grid  from  the  telephone  transmitter.  This  action,  therefore,  prevents 
control.  This  would  render  the  system  inoperative,  but  the  effect  is 
avoided  by  the  introduction  of  the  radio  frequency  short-circuit  L'C' 
between  the  grid  and  the  filament,  whereby  no  radio  frequency  potential 
variations  can  occur  on  the  grid. 

Another  form  of  the  same  general  type  is  shown  in  Figure  178.    In 
this  form  also  the  control  system  of  energy  absorption  by  the  pliotron  is 


FIGURE  178 — General  Electric  Company-Alexanderson  alternator-pliotron  control 

radiophone  transmitter. 

used,  but  in  addition  an  appropriate  radio  frequency  transformer  LLr 
is  provided.  This  raises  the  applied  voltage  to  a  value  most  suitable  for 
the  pliotron  actually  available.  In  other  words,  instead  of  absorbing  a 
given  amount  of  energy  at  low  voltage  and  high  current  it  is  absorbed 
at  high  voltage  and  low  current.  Furthermore,  there  are  provided  two 
plates  PI  and  P*>  of  the  pliotron  so  that  absorption  occurs  during  both 
half  cycles.  The  actual  appearance  of  the  step-up  transformer  which  has 
been  used  experimentally  is  given  in  Figure  179.  It  is  an  open  core  auto- 
transformer  consisting  of  a  number  of  flat  coils  hung  on  wooden  rods. 
One  or  two  of  the  central  sections  are  tapped  to  form  the  primary  and 
the  whole  set  of  coils,  terminating  at  wires  X9  Y  constituted  the  second- 
ary. Special  forms  of  end  shields  designed  to  prevent  excessive  corona 
and  break-down  are  mounted  at  the  ends  of  these  sets  of  coils.  The 
exact  mode  of  operation  of  this  transformer  is  described  in  ' '  Proceedings 
of  the  Institute  of  Radio  Engineers,"  Volume  3,  number  2,  page  138. 


180  Alexanderson's  Pliotron  Absorption  System 

This  transformer  has  very  low  losses,  so  that  it  becomes  possible  to  trans- 
form from  250  volts  to  100.000  volts  at  100,000  cycles.  Under  these 
conditions,  the  inductance  of  the  transformer  system  was  such  that  2 
amperes  appeared  at  the  center  of  the  secondary  winding.  A  study  of 
the  action  of  this  transformer  shows  that  if  the  decrement  of  the  sec- 
ondary tuned  circuit  be  increased  (by  the  pliotron)  from  its  normal  value 
of  about  0.008  to  about  0.8,  the  effective  impedance  of  the  system  will 


.J 


FIGURE  179 — Step-up  transformer  for  radio-frequency 
high  voltage  transformation. 


increase  from  125  ohms  to  12,500  ohms.  One  unusual  characteristic  of 
this  method  of  varying  the  radio  frequency  resistance  of  the  antenna, 
by  inserting  therein  the  primary  of  a  transformer  the  secondary  circuit 
of  which  contains  a  pliotron,  is  that  maximum  secondary  current  natural- 
ly corresponds  to  minimum  antenna  current. 

This  system  of  control  enabled  radiophone  communication  between 
Schenectady  and  Pittsfield,  a  distance  of  50  miles  (80  km.),  a  small  2 
K.  W.  alternator  running  at  90,000  cycles  being  used  as  the  source. 

Absorption  systems  of  these  types  may  be  used  as  direct,  median, 
or  inverted  modulation  systems.  That  is,  we  may  arrange  so  that,  when 
no  speech  is  taking  place  and  the  microphone  circuit  resistance  is  there- 
fore a  maximum,  the  maximum  current  flows  in  the  antenna;  this  cur- 
rent to  be  suitably  diminished  by  modulation  whenever  speech  begins. 
Or  the  current  in  the  antenna  may  center  about  a  median  value  corres- 


Nature  of  Audio  Frequency  Modulation  181 

ponding,  for  example,  to  half -energy.  Or  finally,  the  antenna  current 
corresponding  to  the  undisturbed  microphone  may  be  practically  zero, 
to  increase  by  modulation  at  the  beginning  of  speech.  This  inverted 
modulation  would  seem  preferable  on  the  basis  of  reduced  radiation 
during  inactive  periods.  However,  only  the  median  modulation  will, 
in  general,  give  satisfactory  articulation. 

One  interesting  point  remains  to  be  mentioned  in  connection  with 
all  modulation  systems.  If  a  100,000  cycle  sustained  wave  be  modulated 
by  a  1,000-cycle  note,  both  theory  and  practice  agree  as  to  the  propriety 
of  regarding  the  modulated  wave  as  the  resultant  of  three  separate  waves: 
namely,  one  corresponding  to  the  frequency  of  100,500,  one  correspond- 
ing to  the  frequency  of  99,500,  and  one  corresponding  to  the  frequency 
of  100,000.  All  three,  being  physically  present,  are  detectable  with  a 
wave  meter,  and  this  has  a  certain  bearing  on  the  selectivity  in  radio 
telephony,  particularly  at  very  long  wave  lengths,  corresponding  to  low 
radio  frequencies. 


CHAPTER  VIII. 

(h)  FERROMAGNETIC  CONTROL  SYSTEMS;  EXPERIMENTS  OF 
KUHN;  MULTIPLE  MICROPHONE  PRELIMINARY  CONTROL; 
RADIO  FREQUENCY  CHOKE  COIL  COMBINATIONS;  TELEFUN- 
KEN  COMPANY  TRANSMITTERS;  ALEXANDERSON  TELEPHONE 
BELAY;  ALEXANDERSON  MAGNETIC  AMPLIFIER;  MAGNETIC 
AMPLIFIER  CIRCUITS;  MAGNETIC  AMPLIFIER  CHARACTER- 
ISTICS OF  CONTROL  AND  STABILITY;  WORK  OF  GENERAL 
ELECTRIC  COMPANY,  (i)  COMPARISON  OF  CONTROL  SYSTEMS 
FOR  Low  POWERS,  FOR  MODERATE  POWERS,  FOR  HIGH  POWERS. 

(h)  FERROMAGNETIC   CONTROL   SYSTEMS. 

We  pass  now  to  a  highly  valuable  group  of  control  systems  wherein 
the  magnetic  properties  of  the  iron  cores  of  inductances  are  utilised. 
They  depend  on  the  following  principle.  The  permeability  of  iron  is  not 
constant;  that  is,  the  magnetic  flux  or  induction  through  the  iron  core 
of  an  inductance  is  not  directly  proportional  to  the  applied  magnetising 


rn   r 

T~  K^)-1          ' — ^¥ 


FIGURE  180 — Control  of  radio  frequency  current  in  resonant  circuit  by  variation 
of  magnetisation  of  iron  core  of  inductance. 


force  (in  ampere  turns)  but  varies  in  the  manner  which  was  discussed 
in  the  description  of  Figure  107,  page  110,  though  in  connection  with  a 
different  application  to  frequency  changers.  In  consequence,  the  in- 
ductance of  such  a  coil  is  dependent  on  the  current.  Starting  with  very 
small  magnetisation,  the  permeability  rapidly  increases  to  a  maximum 
and  then  slowly  drops  till  it  reaches  the  value  unity  for  very  high  flux 

182 


Ferromagnetic  Control  System  of  Dr.  Kiihn 


183 


densities.  Similarly,  beginning  with  a  small  current  through  an  iron 
core  inductance,  the  inductance  of  the  coil  first  rises  rapidly,  and  then 
drops  slowly.  This  point  will  be  illustrated  hereafter. 

We  shall  consider  only  two  radiophone  systems  based  on  this  prin- 
ciple, since  these  two  are  the  only  ones  in  actual  use  at  present.  They 
are  the  system  of  the  Telefunken  Company,  as  devised  by  Dr.  Ludwig 
Kiihn  and  others,  and  the  General  Electric  Company 's  system,  as  devised 
by  Mr.  E.  F.  W.  Alexanderson. 


10 


600 


//OO 


Ampere  Turns 
(i2  x  turns) 


FIGURE     181 — Control     characteristic     of 

resonant  circuit  containing  iron  core 

inductance  of  variable 

magnetisation. 

Dr.  Kiihn  was  led  to  work  out  the  first  mentioned  system  by  his 
failure  in  1912  to  control  directly  approximately  7  kilowatts  of  radio 
frequency  energy  by  72  microphones !  The  first  circuit  devised  by  him  is 
shown  in  Figure  180.  Here  circuit  2  contains  the  radio  frequency 
alternator  G  and  the  primary  P  of  an  ordinary  transformer.  We  shall 
call  the  current  in  this  circuit  ^.  The  next  circuit,  1,  contains  the  sec- 
ondary S  of  the  same  transformer,  an  iron  core  inductance  Slt  a  tuning 
condenser  (7,  and  the  ammeter  A.  In  this  circuit  we  have  the  current  iy 
Circuit  3  contains  the  battery  B,  a  variable  resistance  R,  the  ammeter 
A',  two  choke  coils,  L  and  L ',  to  prevent  radio  frequency  currents  flow- 
ing in  this  circuit  by  induction  from  $x  to  M,  and  the  magnetising  coil  M. 
If  circuit  1  be  tuned  to  resonance  and  then  circuit  3  be  closed,  the  in- 
ductance of  Si  will  be  changed  because  of  the  change  in  permeability  of 
the  iron  core.  In  consequence,  the  current  in  circuit  1  will  drop  as  the 
direct  current  in  circuit  3  is  increased.  Conversely,  we  might  arrange 


184 


Ferromagnetic  Control  Characteristics 


to  have  full  resonance  current  in  circuit  1  with  a  moderate  direct  current 
flowing  through  M,  and  in  this  case  diminishing  (or  increasing)  the 
direct  current  would  cause  the  alternating  current  in  circuit  1  to  drop. 
This,  then,  is  a  system  whereby  the  radio  frequency  current  in  circuit  1 
may  be  caused  to  follow  variations  in  the  current  in  circuit  3. 

The  control  characteristic  of  a  somewhat  improved  system  of  this 
type  shown  in  Figure  183,  is  given  in  Figure  181.  Vertically 
is  plotted  the  radio  frequency  current  in  the  antenna  and  horizontally 
the  magnetising  force  (i.  e.,  the  product  of  amperes  and  turns).  It  will 
be  seen  that  the  control  is  linear  between  point  A  (corresponding  to  10 
amperes  antenna  current)  and  C  (corresponding  to  40  amperes).  A 


BC 


FIGURE  182 — Iron  magnetisation  curve. 

change  in  ampere  turns  of  1,100  -  600  or  500  is  necessary  to  effect  this 
change  in  antenna  current.  The  reason  why  the  curve  of  Figure  181 
bends  at  C  is  shown  in  Figure  182,  which  is  the  magnetisation  curve 
of  the  iron  core  of  the  controlling  inductance.  It  will  be  seen  that  the 
control  must  be  much  more  effective  for  magnetising  currents  lying 
between  the  value  OA  and  OB  than  for  values  lying  between  OB  and  00, 
since  the  difference  between  BE  and  AD  is  considerably  greater  than 
the  difference  between  CF  and  BE. 

A  control  system  of  the  type  shown  in  Figure  180  will  be  most 
effective  under  the  following  conditions.  (By  effectiveness  is  meant 
a  maximum  change  in  the  alternating  current  is  for  a  given  change  in 
the  direct  current  i.2.) 

1.  When  a  given  amount  of  change  of  direct  current  energy  in 
circuit  3  causes  the  greatest  possible  change  in  the  inductance  of  $x; 


Ferromagnetic  Control  of  Telefunken  Company 


185 


2.  When  the  damping  of  circuit  1  is  a  minimum,  so  as  to  give  sharp 
resonance  phenomena ; 

3.  When  the  couplings  between  the  various  circuits  are  suitably 
adjusted ; 

4.  When  the  ratio  of  the   continually  present  inductance  in  the 
circuit  1  to  the  variable  component  of  inductance  in  that  circuit  is  a 
minimum.    Some  of  these  requirements  are  incompatible  with  each  other. 
For  example,   requirements  2  and  4  may  easily  conflict.     A  rational 
compromise  must  then  be  effected.    As  far  as  requirement  2  is  concerned, 


FIGURE  183 — Telefunken  Company-Kiihn  system  of  antenna 
current  control. 


this  will  require  the  use  of  very  thin  sheets  of  special  iron  as  the  core 
of  the  inductance  St.  In  fact,  sheets  0.001  inch  (0.02  mm.)  to  0.002  inch 
(0.04  mm.)  are  recommended  for  this  use. 

An  improvement  on  the  system  of  control  shown  in  Figure  180  is 
given  in  Figure  183.  It  will  be  seen  that  in  this  case  the  magnetising 
coil  M  controls  the  inductance  P  of  the  radio  frequency  alternator 
circuit  and  also  the  inductance  8  in  the  antenna  circuit.  Consequently 
both  circuits  may  be  detuned  and  the  resulting  change  in  antenna  cur- 
rent for  a  given  change  in  magnetising  current  i2  will  be  considerably 
enhanced. 


186 


Multiple  Microphone  Preliminary  Control 


A  further  study  of  Figure  181  will  indicate  that  the  portion  AC 
of  the  control  characteristic  should  be  as  long  as  possible,  and  as  straight 
and  steep  as  possible.  It  was  feared  at  first  that  working  with  iron  core 
inductances  in  the  radio  frequency  circuits,  hysteresis  effects  might  distort 
the  speech  so  as  to  make  it  unrecognisable.  Experiment,  which  is  an  un- 
failing criterion  in  such  matters,  demonstrated  conclusively  that  this  fear 
was  groundless.  Care  must  be  taken,  however,  not  to  exceed  the  limits  of 
antenna  current  imposed  by  the  straight  line  portion  of  the  control  char- 
acteristic. For  an  actual  characteristic  given  in  Figure  181,  the  change 
in  antenna  energy  between  10  amperes  and  40  amperes  would  be  5.4 
k.w.  with  the  antenna  used.  In  use  for  radio  telephony,  a  somewhat 
more  limited  range  of  control  was  used. 


o 


-WWVWH 


JWWWW-' 


FIGURE    184 — Telefunken    Company-Kiilm   system   for 
utilising  microphones  in  parallel  on  direct  current. 


In  order  to  secure  the  necessary  control  speech  current,  Dr  Kiihn 
devised  the  series-multiple  arrangement  of  microphones  shown  in  Figure 
184.  This  is  considered  at  this  point  instead  of  under  "Microphone 
Control  Systems"  because  no  radio  frequency  energy  is  supposed  to 
pass  through  the  microphones  and  they  control  only  indirectly  through 
a  ferromagnetic  inductance.  Each  of  the  microphone  banks  .¥„  M2,  M3 
is  fed  from  the  same  generator  0  and  through  its  individual  large 
resistance  Rlt  R2,  R3.  Across  each  microphone  is  shunted  the  primary 
P  of  the  telephone  current  step-down  transformer  and  the  corresponding 
one  of  the  three  condensers  <717  C.2,  <73.  The  output  is  taken  from  XY. 


Radio  Frequency  Choke  Systems 


187 


The  action  is  simple.  Whenever  the  microphone  resistance  increases, 
the  current  through  its  series  resistance  remains  nearly  constant  but 
the  current  through  it  diminishes.  The  excess  current  tends  to  find 
its  way  through  P  and  the  corresponding  condenser.  This  arrangement 
of  microphones  is  easily  seen  to  be  stable.  The  telephone  transformer 
PS  must  be  carefully  designed.  In  practice  it  is  a  10-to-l  step-down 
transformer  with  a  total  iron  path  of  about  13  cm.  (5  inches).  The 
primary  and  secondary  volt-amperes  are  nearly  equal,  the  leakage, 
resistance,  iron  losses,  and  magnetising  current  being  all  reduced  to  a 
minimum. 

It  will  be  noticed  from  Figure  183  that  there  is  a  marked  tendency 
to  induce  radio  frequency  currents  in  the  magnetising  circuit  including 
M,  since  M  is,  in  effect,  the  secondary  of  a  transformer  of  which  P  is 


a 


L       f  L 
Lf^Ls'L, 


V 


FIGURE  185 — Ordinary  and  Telefunken  Company-Kiihn  radio 
frequency  choke  systems. 

the  primary.  Drastic  means  must  be  taken  to  avoid  this  because  of  the 
damage  to  the  battery  and  microphones  which  would  be  done  and  the 
loss  of  output  energy  resulting.  In  Figure  183  ordinary  iron  core 
choke  coils  are  indicated  as  the  means  whereby  the  radio  frequency 
currents  are  choked  off,  but  this  means  would  almost  always  be  entirely 
insufficient.  The  distributed  capacity  of  such  a  coil  would  cause  it  to 
interpose  but  little  impedance  to  the  radio  frequency  current,  in  general. 
A  more  usual  means  is  by  the  use  of  the  loop  circuit  shown  in  the  left 
of  Figure  185.  As  is  well  known,  the  reactance  of  such  a  loop  measured 
between  the  points  U  and  V  becomes  infinite  at  the  frequency  for  which 
the  loop  is  resonant,  provided  there  are  no  losses  in  L  and  C.  Even  if 


188 


Radio  Frequency  Choke  Systems 


there  are  small  losses  in  L  and  C,  the  impedance  will  become  very  high. 
An  improved  method  whereby  unusually  high  impedances  can  be  secured 
by  the  coils  used  in  practice  is  shown  in  the  right  hand  portion  of  Figure 
185.  Here  L^  and  L2  are  two  coils  wound  in  opposite  directions  on  the 
same  core  (not  of  iron).  I!  and  L"  are  small  inductances  widely  sep- 
arated from  each  other.  L3  and  L±  constitute  a  double  coil  similar  to 
LI  and  L*>.  The  tuning  condenser  C'  is  inserted  as  shown.  For  the 
audio  frequency  telephone  currents,  Ll  and  L2  form  a  system  of  very 


FIGURE  186 — Telefunken  Company-Kuhn  radiophone  transmitter,  1913. 

low  inductance  as  do  Lz  and  L4.  In  fact,  the  inductance  between  V 
and  V  for  telephone  currents  is  only  20  microhenrys  in  one  practical 
instance.  On  the  other  hand,  for  the  radio  frequency  currents  the  im- 
pedance is  extremely  high. 

The  latest  and  most  improved  pattern  of  these  radiophone  sets  is 


Telefunken  Company  Radiophone  Transmitter 


189 


FIGURE  187 — Telefunken  Company  10  k.w.  alternator-frequency  doubler 
radiophone  transmitter. 


190  Telefunken  Company  Radiophone  Transmitter 

shown  in  outline  in  Figure  186.  As  will  be  seen,  the  generator  G  of 
radio  frequency  energy  is  placed  in  a  tuned  circuit  including  C  and  the 
primaries  P1  and  P2  of  the  frequency  changers.  (A  description  of  these 
frequency  changers  has  already  been  given  in  connection  with  Figures 
107  through  111,  page  110.)  The  secondaries  ^  and  82  of  the  frequency 
changers  are  in  the  antenna  circuit  in  series  with  a  necessary  tuning 
inductance.  The  direct  current  generator  Gl  is  arranged  to  supply  the 
direct  current  magnetisation  of  the  frequency  changers  by  the  coils  H1 
and  M2.  The  two  gaps  in  the  circuit  of  this  generator  at  UV  are  sup- 
posed to  be  filled  with  choke  systems  such  as  those  of  Figure  185,  the 
lettering  corresponding.  The  telephone  control  current  produces  changes 
in  the  otherwise  constant  magnetisation  of  the  frequency  changer  cores 
in  passing  through  the  coils  M'  and  W.  The  telephone  currents  origin- 
ate in  the  gap  XY  which  corresponds  to  the  terminals  XY  of  Figure  184, 
the  remainder  of  the  microphone  system  being  omitted  from  Figure  186 
for  the  sake  of  simplicity.  For  the  same  reason,  the  choke  systems  at 
points  UV  in  the  telephone  control  circuit  are  only  indicated.  It  will 
be  noted  that  the  system  here  shown  differs  from  the  simpler  system  of 
Figure  183,  not  only  in  the  use  of  the  frequency  changers  but  also  in 
the  separate  constant  direct  current  magnetisation  and  separate  tele- 
phone control  current  magnetisation.  Instead  of  having  only  one  set 
of  frequency  changers,  the  terminals  FH  may  themselves  be  the  output 
terminals  of  one  or  more  frequency  changers  these  being  placed  where 
the  generator  G  is  indicated. 

An  actual  radiophone  set  of  this  type  is  shown  in  Figure  187.  This 
set  is  supposed  to  be  run  from  110-volt  direct  current  mains.  A  motor 
drives  the  10  K.W.,  10.000  cycle  alternator,  which  is  similar  to  that 
shown  and  explained  in  connection  with  Figures  112  and  113,  page  114. 
The  frequency  may  be  raised  in  four  steps  to  160,000  cycles  correspond- 
ing to  1,880  meters  wave-length.  In  the  middle  of  the  top  crown  panel 
is  a  control  stroboscope  for  watching  the  telephone  control.  This 
device  is  a  small  neon  or  carbon  dioxid  vacuum  tube  rapidly  rotated  by 
a  small  motor.  It  is  connected  through  a  small  capacity  to  a  high 
potential  point  of  the  antenna  system,  and  when  there  is  sustained  radia- 
tion, a  uniform  circular  band  of  light  caused  by  the  rotating  tube  in- 
dicates this  fact.  If  a  musical  sound  affects  the  microphone  transmitter, 
the  circular  band  of  light  is  broken  into  narrow  radial  bands,  and  the 
relative  brightness  of  the  center  of  the  bands  and  the  darkness  of  the 
middle  of  the  space  between  them  indicates  very  roughly  the  complete- 
ness of  the  modulation.  However,  such  instruments  are  far  from  quan- 
titative, being  at  best  rough  indicators.  The  top  row  of  instruments 
are  respectively  for  the  direct  current  supply  voltage,  the  current  sup- 


Telefunken  Company  Radiophone  Transmitter 


191 


plied  a  special  small  motor,  the  excitation  (field)  direct  current,  the 
80,000  cycle  telegraph  control  key  circuit,  and  a  O-to-40  ampere  antenna 
ammeter.  The  second  row  of  instruments  are  the  large  motor  ammeter, 
the  "magnetising"  current,  an  80-ampere  ammeter  for  the  10,000  cycle 
output  circuit,  a  10-ampere  ammeter  for  indicating  the  alternating 
current  from  the  microphone  transformer  (corresponding  to  XY  of 
Figure  184),  and  the  antenna  current  ammeter  for  telephony.  The 
lower  left  panel  carries  the  large  driving  motor  switch,  the  magnetising 
current  switch,  and  control  switches  and  fuses  for  the  stroboscope  and 


FIGURE    188 — General    Electric    Conipany- 

Alexanderson  telephone  control 

relay ;  rotor. 

the  ventilating  fan  motor.  The  center  lower  panel  carries  the  key  relay 
(for  telegraphy),  a  field  rheostat,  the  frequency  regulating  device  of 
the  musical  tone  producer  for  ordinary  telegraphy  (simulating  a  spark 
station),  and  the  wheels  which  control  the  tuning  inductances  (vario- 
meters) of  the  10,000  cycle  circuit,  the  40,000  cycle  circuit,  and  the 
80,000  cycle  key  circuit.  On  the  right  hand  lower  panel  are  the  control 
wheels  of  the  inductances  in  the  20,000,  80,000,  and  160,000  cycle  (an- 
tenna) circuits,  the  frequency  meter  for  musical  tone  telegraphy,  and 
8  or  10  microphones  suitably  arranged.  The  desk  carries  the  telegraph 
key  and  the  bottom  panel  to  its  left  the  motor  starters  and  regulators. 


192  Experiments  of  Telefunken  Company 

The  entire  outfit  can  put  about  6  kilowatts  into  the  antenna  at  1,900 
meters  for  telegraphy  and  several  kilowatts  for  telephony.  Some  figures 
given  by  Dr.  Kiihn  indicate  that  a  microphone  output  of  about  4  watts 
(or  20  volt-amperes),  corresponding  to  a  control  alternating  current 
of  8  amperes  through  the  30  turns  of  the  40  microhenry  control  wind- 
ings on  the  final  transformers,  suffices  to  control  several  kilowatts,  the 
energy  amplification  being  as  great  as  1,000. 

With  a  set  similar  to  that  shown,  using  the  Nauen  antenna  and 
at  a  wave-length  near  5,000  meters,  speech  was  transmitted  from  Berlin 
to  Vienna,  a  distance  of  340  miles  (550  km.),  the  received  words  hav'ng 


FIGURE    189 — General    Electric    Company- 

Alexanderson  telephone  control  relay ; 

stator    (field  and  armature). 

an  audibility  of  100.  Professor  Kann,  listening  at  Vienna,  stated  that 
there  were  unusually  heavy  atmospheric  disturbances.  The  speech  was 
clear  but  the  vowels  were  emphasized  while  the  consonants  seemed 
sometimes  to  be  almost  missing.  On  the  other  hand,  singing  was  fault- 
lessly transmitted.  How  far  these  effects  were  due  to  the  heavy  strays 
and  how  far  to  iron  distortion  of  the  speech  forms  is  not  stated. 

We  consider  next  a  further  development  of  the  ferromagnetic 
control  systems,  namely  Mr.  Alexanderson 's  magnetic  amplifier  as  de- 
signed for  the  General  Electric  Company.  Prior  to  considering  this 
device,  the  parent  idea  from  which  it  sprang  will  be  given.  This  was  a 
so-called  "telephone  relay,"  It  was  a  moderately  high  frequency 


Alexanderson  "Telephone  Relay" 


193 


alternator  of  the  inductor  type  the  field  of  which  was  varied  by  the 
speech  current.  In  consequence  the  output  of  the  machine  was  similarly 
modulated.  The  rotor  of  the  machine  is  shown  in  Figure  188.  The 
iron  teeth  had  to  be  laminated  because  of  the  variations  in  the  field  pro- 
duced by  the  speech  current.  This  was  a  serious  limitation  of  the 
machine.  The  stator  of  the  machine  is  similarly  shown  in  Figure  189. 
The  zig-zag  winding  of  the  alternator  around  the  teeth  is  clearly  visible. 
Underneath  this  winding  are  field  windings.  To  avoid  the  limitation 
mentioned  above,  the  modern  magnetic  amplifier  was  invented,  this 
being  a  device  which  has  practically  the  same  effect,  when  placed  across 
the  terminals  of  a  radio  frequency  alternator,  as  would  speech  variation 
of  the  field  thereof. 


50 


JO 


ifaatiLx* 

ffurtxnf/t 


Indvctireload 


1O 


.20 


40 


FIGURE  190 — Load  characteristics  of  50  K.  W.,  50,000  cycle  Alexanderson 

alternator. 


Let  us  consider  first  the  operating  characteristics  of  an  Alexanderson 
radio  frequency  alternator,  namely  the  50  k.w.,  50,000  cycle  machine 
shown  in  Figure  124,  page  124.  These  characteristics  are  shown  in 
Figure  190.  It  will  be  seen  that  if  50  ohms  of  external  resistance  are 
shunted  across  the  machine  terminals,  the  current  (at  the  point  W) 
will  be  17  amperes.  As  this  load  resistance  is  diminished,  the  current 
rises  along  the  dashed  curve  to  the  point  $.  This  corresponds  to  zero 
resistance  across  the  alternator  and  to  a  current  flow  of  63  amperes. 
This  current,  since  the  load  is  a  pure  resistance,  is  in  phase  with  the 
voltage  (neglecting  machine  impedance),  and  the  curve  has  been  repeated 
symmetrically  to  the  left  of  the  current  axis  by  the  curve  QX.  If  various 
reactances  (in  the  form  of  resistance-free  inductance)  are  placed  across 


194 


Load  Characteristics  of  Alexanderson  Alternator 


the  terminals  of  the  machine,  the  curve  QV  is  obtained  for  the  relation 
between  current  and  external  reactance  in  ohms.  Thus  the  point  V 
corresponds  to  50  ohms  reactance  or  0.00016  henry  at  50,000  cycles. 
The  current  in  this  case  lags  behind  the  electromotive  force  since  the 
load  is  inductive.  If  50  ohms  of  capacity  reactance,  which  corresponds 
to  0.064  microfarad  at  50,000  cycles,  and  is  indicated  at  the  point  U,  be 
placed  across  the  machine,  a  current  of  24  amperes  is  obtained.  As 
the  external  capacitive  reactance  is  diminished,  the  current  increases, 
reaching  a  maximum  of  71  amperes  at  8  ohms  corresponding  to  0.40 
microfarad  at  50,000  cycles.  On  leaving  the  point  P  of  maximum  cur- 
rent, with  diminishing  external  reactance  and  corresponding  external 


tooo 


6QG 


MO- 


ZQQ 


600 


8M 


MM 


Loac 


40    50    6,9X7-)    89 


l\ 


FIGURE    191 — Load    characteristics   of   50 

K.  W.,  50,000  cycle  Alexandersou 

alternator. 

capacity  load,  the  curve  drops  again  to  the  point  Q.  In  the  portion  QPU 
of  the  curve,  the  current  leads  the  voltage  since  the  load  is  capacitive. 
It  will  be  seen  that  the  curve  UPQV  is  nothing  more  than  the  resonance 
curve  of  the  system  made  up  of  the  alternator  armature  and  the 
external  load.  Since  the  capacity  reactance  for  resonance  is  8  ohms, 
the  inductive  reactance  of  the  alternator  armature  must  have  the  same 
numerical  value.  Consequently  the  inductance  of  the  armature  must 
be  approximately  26  microhenrys  at  50,000  cycles,  an  interestingly  low 
value. 


General  Electric  Company  Magnetic  Amplifier 


195 


The  same  material  is  plotted  in  another  fashion  (based  on  the  curves 
given  by  Mr.  Alexanderson  in  an  earlier  publication)  in  Figure  191. 
The  curves  given  differ  from  those  of  Figure  190  only  in  that  alternator 
terminal  volts  and  load  current  are  plotted  instead  of  external  impedance 
and  load  current.  It  may  be  noted  that  the  0  per  cent,  power  factor 
curve  is  that  of  a  pure  inductive  or  capacitive  load;  that  is,  one  which 
is  resistance-free.  In  the  same  way,  the  100  per  cent,  power  factor 
resistance  curves  are  with  a  load  consisting  of  nothing  but  resistance. 
While  not  quite  so  clearly  visible,  the  resonance  phenomenon  is  indicated 
here  also. 

The  general  arrangement  of  the  magnetic  amplifier  in  its  simplest 
form  are  represented  in  Figure  192.  The  nature  of  the  iron  structure 
is  sufficiently  indicated.  Coils  Ll  and  L2  are  wound  over  the  two  middle 


FIGURE  192 — General  Electric  Company- Alexanderson  magnetic 

amplifier  (shunt  connected  to  alternator,  multiple 

connection  of  coils). 

cores,  connected  in  parallel,  and  the  combination  shunted  across  the 
radio  frequency  alternator  A.  (Coils  Lx  and  L2  are  placed  in  parallel 
rather  than  in  series  since  theory  and  experiment  agree  in  predicting 
a  more  effective  control  by  such  connection.)  It  will  thus  be  seen  that 
the  iron  core  inductance  L:  L2  is  placed  across  the  alternator  terminals. 
If  this  inductance  is  varied  by  any  means,  the  right  hand  curve  of 
Figure  190  will  indicate  the  current  variation  through  the  inductance. 
Consequently  the  antenna  current  will  also  vary  in  the  opposite  sense,  and 
a  marked  degree  of  antenna  current  control  would  be  thus  obtained.  The 
mode  of  varying  the  inductance  of  coils  L±  and  L2  is  also  shown  clearly 
in  Figure  192.  It  is  by  means  of  the  coil  L3  through  which  passes  a 
direct  current  from  the  battery  B  which  current  can  be  suitably  varied 
by  the  control  resistance  R.  It  will  be  seen  that  L3  is  wound  over  the 
cores  of  both  Lx  and  L2  and  thus  there  will  be  therein  no  radio  frequency 


196 


Magnetic  Amplifier  Structure 


induction  from  the  latter.  This  is  important,  and  constitutes  .a  marked 
advantage  of  Mr.  Alexanderson 's  magnetic  amplifier  over  the  device 
used  by  the  Telefunken  Company  and  shown  in  Figure  186.  The  actual 
appearance  of  the  amplifier  is  given  by  Figure  193.  The  magnetising 
control  coils  L3  are  indicated  as  in  Figure  192.  The  two  sets  of  coils  cor- 
responding to  L!  and  L2  are  also  indicated.  The  coils  Lt  are  partly 
hidden  by  the  cross  piece.  It  may  be  mentioned  that  a  number  of 
further  designs  of  more  advanced  character  have  been  adopted  recently 


FIGURE  193 — General  Electric  Company-Alexanderson 
"magnetic  amplifier"  radiophone  control. 

for  the  magnetic  circuits  of  the   amplifier,  but  the  principle  remain^ 
unchanged. 

The  actual  behavior  of  the  amplifier  is  well  represented  by  Figure 
194.  This  shows  the  impedance  of  the  amplifier,  expressed  in  ohms, 
plotted  against  the  radio  frequency  current  passing  through  it  for 
various  direct  currents  through  the  magnetising  coils  L3.  It  will  be 
seen  that  for  no  magnetisation  (curve  ABC)  the  impedance  varies  from 
32  to  70  ohms  between  60  amperes  of  radio  frequency  current  and  20 
amperes.  "With  0.7  ampere  d.  c.  magnetisation,  the  variation  is  some- 
what in  the  opposite  sense,  namely  between  27  ohms  and  15  ohms  for 


Magnetic  Amplifier  Characteristics 


197 


FIGURE  194 — Characteristics  of  Alexanderson  Magnetic  Amplifier. 

the  variation  of  radio  frequency  current  between  60  and  10  amperes. 
For  2.0  amperes  magnetisation  current,  the  impedance  of  the  amplifier 
remains  nearly  constant  around  8  ohms  for  the  same  extreme  variation 
of  radio  frequency  current  through  it.  Considering  the  line  ADGK, 
it  is  clear  that  with  60  amperes  radio  frequency  passing  through  it, 
the  amplifier  impedance  changes  from  32  ohms  to  8  ohms  as  the  direct  cur- 
rent magnetisation  is  increased  from  0  to  2.0  amperes.  Similarly,  at  55 
amperes  radio  frequency  current  through  the  amplifier,  corresponding 
to  line  JTY,  a  somewhat  wider  variation  is  obtained.  It  is  thus  perfectly 


Wl? 


1200. 


.422 


7 


0.7 


FIGUBE    195 — Characteristics    of    Alexanderson 
magnetic  amplifier. 


198 


Magnetic  Amplifier  Series  Condenser 


clear  that  the  amplifier  is  a  markedly  effective  device  as  a  variable  im- 
pedance for  radio  frequency  currents.  The  same"  data  as  that  represented 
in  Figure  194  is  given  in  different  form  in  Figure  195,  which  gives  the 
corresponding  voltage-current  curves  of  the  amplifier.  It  will  be  seen 
that  the  current  through  the  amplifier  at  400  volts  impressed  radio 
frequency  may  be  varied  from  5  amperes  (for  no  d.c.  magnetisation) 
to  50  amperes  with  2.0  amperes  magnetisation.  At  1,200  volts  applied 
radio  frequency,  a  current  variation  of  15  to  60  amperes  (i.  e.,  from  18 
to  72  kilo  volt  amperes)  is  obtained  with  a  variation  of  the  i.e.  magnetisa- 
tion of  only  1  ampere,  a  full  illustration  of  the  usefulne^  of  the  device. 


HI 


G. L 


L, 


A 


B 


FIGURE    196 — General    Electric  -  Company- Alexanderson   magnetic    am- 
plifier, with  series,  short-circuiting,  and  shunt  condensers. 


In  order  to  secure  the  maximum  linear  control  and  to  prevent  cer- 
tain undesired  effects,  several  condensers  are  inserted  into  the  amplifier 
circuits  as  shown  in  Figure  196.  The  first  of  these  is  the  series  con- 
denser Cj.  which  is  placed  between  the  high  potential  point  of  the  alterna- 
tor and  a  point  leading  to  one  side  of  the  amplifier  (through  several 
other  condensers  to  be  considered  below).  The  effect  of  the  series  con- 
denser on  the  stability  of  operation  of  the  amplifier  and  otherwise  is 
illustrated  in  Figure  197.  This  curve  shows  the  current  flowing  from  the 
alternator  as  ordinate  plotted  against  the  external  impedance  in  ohms. 
The  dot-and-dash  curve  shows  the  effect  of  a  purely  inductive  load  and 


Stability  of  Magnetic  Amplifier 


199 


is  the  same  as  curve  QV  of  Figure  190.  The  dashed  curve  for  the  ampli- 
fier alone  is  not  far  from  curve  ABC  of  Figure  194.  To  the  left  of  the 
vertical  axis  is  drawn  the  corresponding  curve  of  the  constant  impedance 
of  8  ohms,  this  being  a  capacity  of  0.33  microfarad.  The  curve  in 
question  is  the  vertical  line  marked  0.33  /xf.  Inserting  such  a  con- 
denser at  Cl  will  give  the  resulting  curve  to  the  right  marked  "amplifier 
+  0.33  fj.f. "  This  curve  represents  a  stable  state  of  affairs.  At  the  ex- 
treme left,  the  vertical  dashed  line  shows  the  constant  impedance  of  48 
ohms  corresponding  to  a  series  condenser  of  0.067  microfarad.  The  curve 
marked  "amplifier  -|-  0.067.  /xf. "  is  the  result  of  using  this  series  con- 
denser and  has  an  unstable  portion  to  the  left  of  the  vertical  axis.  This 
corresponds  to  an  increase  of  current  with  an  increase  of  impedance  across 


nsk  tsf-ir  $  c 


2  an  . 


Lo  zd>  vni  t'sfi  7^cf 


.FIGURE  197 — Effect  of  series  condenser  on  stability  of  magnetic  amplifier. 


the  alternator.  The  same  effect  is  shown  in  Figure  198  in  different  form, 
this  figure  representing  alternator  terminal  voltage  vertically  and  cur- 
rent through  the  amplifier  and  condenser  horizontally.  The  curve  marked 
amplifier  +.  0-33  /*f . "  is  a  rising  curve  practically  throughout,  whereas 
the  curve  for  the  "amplifier  -f-  0.125  /if."  shows  a  falling  portion  cor- 
responding to  increasing  current  with  diminishing  voltage.  This  is 
what  we  have  called  a  condition  of  "negative  resistance"  such  as  is 
experienced,  for  example,  in  the  Poulsen  arc.  Accordingly,  this  un- 
stable region  is  unusable  and  may  lead  to  self-excited  oscillation  in  the 
amplifier  system,  which  is  a  normally  undesirable  condition. 


200 


Characteristics  of  Magnetic  Amplifier 


The  effect  of  the  series  condenser  C1  in  Figure  196  is  to  give  a 
great  increase  in  the  sensitiveness  of  the  system  and  also  to  give  a  linear 
control  characteristic.  The  control  characteristics  for  several  values  of 
the  series  condenser  are  shown  in  Figure  199,  which  should  be  carefully 
compared  with  Figures  126  through  128,  page  128.  Curve  A  of  Figure 
199  shows  the  relation  between  antenna  current  in  the  arrangement  of 
Figure  196  and  the  d.c.  amperes  in  the  magnetising  coil  of  the  amplifier 
(L3  in  Figure  196).  It  is  the  real  control  characteristic  of  the  system 


•i&6 


*m 


^teee 


'#6 


406 


2? 


(V 


30 


ff)pi 


7\ 


^WyvaAr&axzfJfrzaX:, 


6? 


aVfyd 


con  ien.  er 


Jcfk 


FIGURE  198 — Effect  of  series  condenser  on  stability  of  magnetic 
amplifier. 

when  used  for  radio  telegraphy  and  telephony.  Curve  E,  obtained  with 
a  series  condenser  of  0.33  microfarad  shows  practically  complete  and 
linear  modulation  except  for  excessive  control  to  the  left  of  the  point  B, 
this  corresponding  to  greater  amplifier  magnetising  currents  than 


Magnetic  Amplifier  Shunt  Condenser 


201 


about  2.8  amperes.  To  the  left  of  this  point  the  control  reverses  as 
indicated  in  Figure  5  which  corresponds  to  this  case.  Between 
Y  and  Z  of  that  figure  we  are  working  on  portion  BD  of  curve  B 
of  Figure  199,  but  between  X  and  Y  of  that  figure  we  are  working 
on  the  reversed  portion  of  curve  B  of  Figure  199.  It  need  hardly  be 
said  that  in  practice  this  condition  can  be  and  is  easily  avoided.  A 
smaller  series  condenser  of  0.125  microfarad  gives  control  characteristic  C 
of  Figure  199.  This  is  a  steeper  control  than  those  of  the  preceding 
cases,  but  it  is  incomplete  and  therefore  not  chosen.  Some  study  will 
convince  the  reader  that  these  control  curves  are  closely  related  to 


80 


60 


'Ser/'es  Ct  mc/cnser 


O.f2y^  f Series  Ct.  nder&er 


"210 

4mpJifter£>.C.£xctfafian,  Amperes. 

FIGURE     199 — Control    characteristics    of    magnetic 
amplifier. 

inverted  resonance  curves  in  a  system  having  moderate  effective  resistance 
and  iron  losses. 

The  second  condenser  considered,  namely,  (74,  in  Figure  196,  is 
known  as  the  shunt  condenser.  Its  function,  according  to  Mr.  Alex- 
anderson,  is  to  cause  the  amplifier  to  take  a  leading,  instead  of  a  lagging 
current  at  low  excitations  and  to  increase  the  sensitiveness  of  the  ar- 
rangement. According  to  Mr.  Louis  Cohen,  it  may  rather  be  treated 


202 


Magnetic  Amplifier  Short-Circuiting  Condenser 


as  forming  with  the  amplifier  a  loop  circuit  the  impedance  and  effective 
resistance  of  which  change  very  markedly  near  a  resonant  frequency. 

The  third  condenser  (actually  the  two  condensers  C2  and  C3)  is 
known  as  the  short-circuiting  condenser.  It  will  be  noticed  that  there  is 
a  closed  circuit  L1C^C3L2  in  which  audio  frequency  currents  may  be 
induced  if  telephonic  currents  flow  in  the  control  winding  L3.  These 
would  be  short-circuited  except  for  the  two  condensers  just  mentioned, 
and  the  control  would  become  ineffective.  The  condensers  C2  and  C3 
are  so  chosen  that  their  audio  frequency  reactance  is  very  high  while 
their  radio  frequency  reactance  is  quite  low.  In  this  way  the  radio  fre- 


FIGUBE  200 — Oscillograms  showing  controlling  telephone  current  and  con- 
trolled antenna  output  of  General  Electric  Company- 
Alexanderson  50  k.w.  alternator  and 
magnetic  amplifier. 

quency  currents  may  still  flow  practically  undeterred  through  the  ampli- 
fier coils  while  the  audio  frequency  currents  are  almost  entirely  pre- 
vented from  doing  so. 

The  combination  of  these  various  condensers  gives  a  high  degree  of 
control.  Experiment  shows  that  the  amplification,  defined  as  the  radio 
of  (maximum  antenna  kilowatts  minus  minimum  antenna  kilowatts) 
divided  by  (effective  kilovolt-amperes  in  the  control  circuit),  varies  from 
100-to-l  to  as  much  as  350-to-l.  This  is  under  the  linear  conditions  neces- 
sary for  control  in  telephony.  The  perfection  of  the  control  is  well 
illustrated  in  Figure  200.  The  lower  oscillogram  shows  the  control  cur- 


Comparison  of  Control  Systems  203 

rent  in  L3  in  Figure  196,  while  the  upper  curve  shows  the  antenna  kilo- 
watts. It  will  be  seen  that  a  variation  of  control  current  of  0.2  ampere 
changes  the  antenna  kilowatts  from  5.8  to  42.7,  a  variation  of  nearly 
37  kilowatts !  The  Author  believes  this  to  be  the  largest  amount  of  radio 
frequency  (or  other)  energy  ever  controlled  by  a  telephone  transmitter. 
It  will  be  noted  that  the  antenna  kilowatt  curve  is  inverted  relative  to 
the  control  current  curve,  the  peaks  in  one  corresponding  to  the  crests 
in  the  other.  This  is  the  result  of  the  control  characteristic  of  Figure 
199,  which  shows  that  large  antenna  currents  correspond  to  small  con- 
trol currents  and  vice  versa. 

(I)  COMPARISON   OF   CONTROL   SYSTEMS. 

The  choice  of  modulation  control  system  will  depend  markedly  on 
the  output  of  the  radiophone  transmitter  and,  to  a  less  degree,  on  the 
type  of  installation,  i.  e.,  ship  or  shore  station,  fixed  or  portable  outfit. 

For  low-power  sets,  the  placing  of  the  microphone  directly  into  the 
antenna  (as  illustrated  in  Figure  10,  page  22)  is  a  simple  solution  and 
one  that  is  economical  of  apparatus.  It  is  not,  however,  economical  of 
energy  since  the  microphone  resistance  for  most  efficient  operation  must 
be  equal  to  that  of  the  remainder  of  the  radiating  system.  This  condi- 
tion necessarily  involves  the  loss  of  half  of  the  available  radio  frequency 
energy  in -the  microphone.  To  some  extent  this- loss  may  be  avoided  by 
the  use  of  one  of  the  circuits  shown  in  Figure  130,  page  133,  whereby 
the  microphone  is  more  fully  utilised  in  that  the  changes  in  its  resistance 
vary  a  number  of  the  electrical  constants  of  the  associated  circuits  and 
thus  produce  greater  proportionate  changes  in  the  antenna  current. 

For  moderate  power  sets,  the  difficulties  in  getting  a  suitable  control 
system  become  quite  serious.  Large  numbers  of  microphones  in  parallel 
are  bulky  and  expensive,  and  tend  to  cause  difficulty  in  adjustment. 
Heavy  current  microphones  seldom  give  the  highest  quality  of  articu- 
lation and  liquid  microphones  are  not  easy  to  build  or  to  shield  from 
disturbance.  On  shipboard  their  use  is  even  less  desirable  than  on  land. 
It  becomes  necessary  to  use  some  type  of  control  based  on  one-way 
amplifiers  (such  as  the  methods  of  the  General  Electric  Company  involv- 
ing absorption  in  pliotrons  as  shown  in  Figures  177  and  178,  page  178, 
and  a  number  of  allied  methods)  or  else  to  use  ferromagnetic  amplifiers. 
These  last  should  be  so  constructed  that  they  are  one-way  devices  so  far 
as  possible,  in  order  that  there  shall  be  no  induction  of  radio  frequency 
currents  in  the  control  or  microphone  circuit. 

For  high  power  sets,  direct  microphone  control  is,  of  course,  out 
of  the  question.  Even  the  use  of  the  normal  vacuum  tube  amplifier 
in  any  of  its  modifications  or  modes  of  use  seems  of  doubtful  utility 
unless  some  very  heavy  output  bulbs  should  be  constructed  in  the  future. 


204  Control  Systems  for  Wire-to-radio  Transfer 

The  most  feasible  methods  at  present  seem  to  be  those  involving  the 
control  of  the  outgoing  energy  by  rugged  ferromagnetic  amplifiers.  The 
control  energy  for  these  amplifiers  may  itself  be  obtained  by  the  use 
of  vacuum  tubes  or  of  smaller  ferromagnetic  amplifiers.  In  other  words 
a  composite  system  depending  on  the  use  of  a  rugged  final  amplifier  is 
desired,  its  control  energy  being  derived  from  a  more  delicate  amplifier 
which  can  be  actuated  by  the  small  amount  of  microphone  energy  actually 
available. 

It  may  be  here  mentioned  that  the  difficulties  of  the  situation  are 
considerably  increased  w7hen  it  is  desired  to  control  the  radiophone  trans- 
mitter from  an  ordinary  wire  telephone  line.  The  power  available  from 
an  ordinary  telephone  line  is  of  the  order  of  microwatts,  whereas  the 
power  derived  directly  from  the  transmitter  may  be  hundreds  or  thou- 
sands of  times  as  much.  The  difference  must  be  made  up  in  the  former 
case  by  at  least  one  audio  frequency  amplification. 


CHAPTER  IX. 

8.  ANTENNAS  AND  GROUND  CONNECTIONS — (a)  RADIATING 
SYSTEMS;  ANTENNA  RADIATION  EFFICIENCY.  9.  RECEPTION 
PHENOMENA,  (a)  DETECTOR  AND  AMPLIFIER  TYPES,  (b) 
BEAT  RECEPTION;  CONSTANCY  OF  RADIATED  FREQUENCY. 
(c)  SELECTIVITY  IN  RECEPTION,  (d)  INTERFERENCE  WITH 
RADIOPHONE  RECEPTION,  (e)  TELEPHONE  RECEIVERS,  (f) 
RECEIVING  APPARATUS  ;  AUDION  RECEIVERS  ;  ARMSTRONG  RE- 
GENERATIVE RECEIVERS;  ULTRAUDION  CIRCUIT;  TELEFUNKEN 
COMPANY;  MEISSNER  RECEIVING  ARRANGEMENTS;  MARCONI 
COMPANY  RECEIVER;  WESTERN  ELECTRIC  COMPANY  TUBES 
FOR  RECEPTION  ;  TUBE  DESIGNS  OF  VAN  DER  BIJL,  NICOLSON, 
AND  HULL  ;  GENERAL  ELECTRIC  COMPANY  TUBES  FOR  RECEP- 
TION AND  AMPLIFICATION  (PLIOTRONS).  (g)  STRAYS;  BAL- 
ANCED VALVE  RECEIVERS;  DIECKMANN  CAGE;  CLASSI- 
FICATION OF  STRAYS;  COMPENSATION  METHOD  OF  STRAY 
REDUCTION;  METHODS  OF  DE  GROOT.  (h)  RANGE  IN  RADIO 
TELEPHONY;  OCCASIONAL  RANGE;  RELIABLE  RANGE;  AN- 
NUAL INCREASE  IN  RANGE. 


8.  ANTENNAS  AND  GROUND  CONNECTIONS, 
(a)  RADIATING   SYSTEMS. 

For  transmission  in  radio  telephony,  much  the  same  requirements 
must  be  met  as  in  the  case  of  a  normal,  sustained  wave,  telegraph  station. 
That  is,  a  high  capacity  antenna  of  low  ohmic  resistance  is  desired.  The 
radiation  resistance  should  be  the  chief  portion  of  the  total  antenna  re- 
sistance else  the  efficiency  of  radiation  may  be  very  low.  This  can  be  well 
illustrated  by  the  following  numerical  example : 

Suppose  an  antenna  to  have  an  effective  height  of  40  meters  (130 
feet),  and  that  1  kilowatt  is  available  for  the  antenna  circuit.  Suppose 
further  that  the  antenna  is  used  successively  at  wave-length  of  1,600, 
3,200,  and  6,400  meters.  In  the  table,  page  206,  are  given  values  of  the 
probable  ohmic  resistance  of  the  antenna,  its  ground  resistance,  and  its 
radiation  resistance  at  each  of  the  wave-lengths.  These  are  calculated 
on  the  basis  that  the  ohmic  resistance  increases  as  the  frequency  increases 

205 


206 


Radiation  Efficiency  of  Antennas 


(i.  e.,  as  the  wave-length  diminishes),  that  the  ground  resistance  dimin- 
ishes almost  inversely  proportionately  to  the  wave-length,  and  that  the 
radiation  resistance  is  inversely  proportional  to  the  square  of  the  wave- 
length. The  antenna  current  is  then  calculated  from  the  total  resistance, 
and  the  radiated  energy  and  radiation  efficiency  in  per  cent. 


Ohmic  Resistance  of  Antenna.  .    .  . 

WAVE  LENGTH 

1,600  m. 

3,200  m. 

6,400  m. 

0.3 
1.0 

1.0 
0.3 
2.6 
19.6 
385. 
39. 

0.2 
2.0 
0.25 
1.2 
3.65 
16.6 
69. 
6.9 

0.1 
4.0 
0.06 

4.8 
8.96 
10.6 
7. 
0.7 

Ground  Resistance  

Radiation  Resistance  

Loading  Coil  Resistance  

Total  Resistance  

Antenna  Current         

Radiated  Power  (watts)  
Radiation  Efficiency  (in  per  cent.) 

It  is  clear  enough,  everything  else  remaining  the  same,  that  the 
shortest  wave-length  (nearest  to  the  antenna  fundamental)  would  be  by 
far  the  most  suitable  so  far  as  radiation  efficiency  is  concerned.  How- 
ever, the  absorption  of  the  electromagnetic  waves  in  passing  over  the 
intervening  country  may  partially  or  entirely  nullify  this  difference, 
and  thus  it  may  occur  that  by  day  and  for  overland  transmission  the  best 
wave  would  not  be  the  1,600  meter  wave  but  possibly  the  3,200  meter 
wave.  For  the  case  mentioned,  with  the  relatively  small  antenna  power 
available,  the  transmission  could  hardly  be  over  a  great  enough  distance 
to  make  the  longest  wave  given  the  most  desirable.  In  other  words,  in 
every  case  of  day  transmission,  there  will  be  some  wave-length  for  which 
best  results  are  obtained  because  a  diminution  of  wave-length  below  this 
most  favorable  value,  while  it  would  increase  the  radiation  efficiency, 
would  more  than  correspondingly  diminish  the  freedom  from  absorption 
in  the  intervening  space. 

In  constructing  antennas  for  radio  telephony,  all  the  usual  precau- 
tions as  to  antenna  insulation,  ground  resistance,  freedom  from  neigh- 
boring energy-absorbing  conductors  and  guy  wires  are  observed.  In  addi- 
tion, it  should  be  remembered  that  it  will  sometimes  be  necessary  to  use 
a  suitable  coupling  between  the  antenna  and  the  radio  frequency  gen- 
erator in  order  that  the  resistance  which  is  thus,  in  effect,  introduced  into 
the  generator  circuit  shall  have  the  most  favorable  value  for  full  generator 
output. 

A  ' '  fly-wheel  effect' '  similar  to  the  ' '  inertia  effect ' '  mentioned  under 
" Causes  of  Distortion  in  Radio  Telephony/'  page  13,  may  occur  in  the 


"Fly  Wheel"  Distortion  of  Speech  207 

antenna  circuit.  If  the  persistency  of  the  antenna  system  is  very  great, 
i.  e.,  if  the  damping  is  very  small,  the  wave  trains  in  the  antenna  will 
tend  to  persist  at  full  intensity  and  the  difficulty  in  getting  complete 
modulation  may  become  excessive.  As  regards  this  feature,  which  is  most 
prominent  at  long  waves,  there  is  a  conflict  between  good  antenna  design 
in  the  usually  accepted  sense  as  indicated  above,  and  the  design  indicated 
to  avoid  the  fly-wheel  effect.  In  general,  however,  the  compromise  will 
be  satisfactory  if  the  fly-wheel  effect  is  practically  disregarded,  except 
for  long  waves  and  very  persistent  antennas. 

(b)  RECEIVING  SYSTEMS. 

The  same  general  considerations  which  were  found  to  hold  for 
transmitting  antennas  also  hold  for  receiving  antennas  except  that 
smaller  antennas  will  in  general  be  used.  This  is  because  of  the 
diminished  expense,  because  of  the  large  static  charges  which  readily 
accumulate  on  large  antennas,  and  because  it  is  easy  enough  to  amplify 
the  signals  received  on  a  small  antenna  to  satisfactory  values.  Of  course, 
the  fly-wheel  effect  mentioned  previously  may  again  occur  in  the  tuning 
of  sharply  resonant  radio  frequency  circuits,  though  the  Author  has  not 
experienced  much  trouble  on  that  score  using  waves  of  moderate  length. 
The  present  tendency  seems  toward  the  use  of  small  antennas  with  sensi- 
tive receiving  sets  and  high  amplification  of  some  sort.  It  seems  that  the 
ratio  of  signal  strength  to  stray  intensity  remains  reasonably  constant  as 
the  size  of  the  antenna  is  diminished,  at  least  when  crystal  detectors  or 
detectors  of  the  audion  type  are  used.  For  the  oscillating  audion,  Mr. 
Armstrong  has  pointed  out  that  this  is  not  necessarily  the  case,  since  the 
oscillating  audion  favors  weak  signals  compared  to  heavy  strays  to  a 
greater  extent  than  does  the  plain  audion.  So  that,  unless  the  beat  method 
is  used  for  reception,  radio  telephonic  reception  may  just  as  well  be 
carried  on  on  small  antennas  as  on  large. 

9.  RECEPTION  PHENOMENA, 
(a)  DETECTOR  AND   AMPLIFIER  TYPES. 

Almost  all  detectors  have  been  used  for  radio  telephony,  and  indeed 
all  but  the  coherer  type  can  be  used.  At  the  present  time  such  detectors 
as  the  crystal  rectifier,  the  audion,  and  the  dynatron  have  proven  to  be 
practically  usable  and  satisfactory.  The  detectors  and  amplifiers  used  in 
radio  telephony  should  have  a  linear  characteristic  like  that  mentioned  in 
connection  with  Figure  6,  page  15.  Otherwise  there  will  be  speech  dis- 
tortion of  the  types  described  in  the  discussion  to  which  reference  has 


208  Radiophone  Beat  Reception 

been  made.  Both  detectors  and  amplifiers  should  be  of  such  sort  that 
they  are  easily  adjusted  to  maximum  sensitiveness,  retain  this  sensitive- 
ness indefinitely,  do  not  require  frequent  renewal,  and  are  inexpensive. 
These  requirements  have  not  yet  been  entirely  met. 

.       <9 

(b)  BEAT  RECEPTION. 

Beat  reception  is  possible  in  radio  telephony,  and  there  may  be  used 
for  this  purpose  either  the  normal  detector  with  an  external  oscillator 
circuit  coupled  to  the  receiving  system  to  produce  the  beats  or  the  so- 
called  "  self  -excited  heterodyne"  where  the  same  vacuum  tube  is  used 
at  once  as  an  oscillator,  detector,  and  amplifier.  Generally  speaking,  this 
latter  arrangement,  while  convenient  in  manipulation  and  economical  of 
equipment,  does  not  utilise  to  the  full  the  various  properties  of  the  bulb 
and  is  less  stable  and  certain  of  adjustment  than  the  former. 

It  need  hardly  be  said  that  for  beat  reception  in  radio  telephony 
extreme  constancy  of  frequency  at  the  transmitting  end  is  essential.  This 
will  be  evident  when  it  is  considered  that  radiophone  reception  under 
these  conditions  requires  either  zero  beats  per  second  (that  is,  equality  of 
frequency  of  the  transmitter  and  of  the  local  oscillator  at  the  receiver) 
or  a  beat  frequency  above  audibility  (that  is,  a  greater  difference  be- 
tween the  transmitter  frequency  and  the  local  oscillator  frequency  than 
say  10,000  cycles  per  second).  As  a  matter  of  fact,  only  the  first  of  these 
expedients  is  practically  usable  since  the  detuning  of  the  antenna  and  its 
associated  circuits  in  the  receiver  for  the  second  case  would  make  the 
reception  very  inefficient  except  on  extremely  short  waves  where  a  differ- 
ence of  frequency  of  10,000  or  more  cycles  per  second  is  only  a  small 
percentage  of  the  main  transmitter  frequency.  However,  it  must  be 
admitted  that  zero  beat  frequency  is  usually  not  very  easy  to  obtain  or 
hold  as  a  receiver  adjustment  and  even  slight  variations  in  transmitter 
or  receiver  oscillation  frequency  will  then  cause  a  drummy  quality  to 
appear  in  the  speech  and  seriously  impair  its  intelligibility. 

With  radiophone  transmitters  employing  alternators,  or  alternators 
and  frequency  changers,  very  perfect  speed  regulation  will  therefore  be 
required  if  beat  reception  is  to  be  used.  For  example,  working  at  6,000 
meters  wave-length  (50,000  cycles  per  second),  a  much  greater  speed 
variation  than  one  part  in  10,000  would  be  objectionable;  and  if  fre- 
quency multipliers  were  employed  in  conjunction  with  the  alternator  to 
get  the  50,000  cycles  per  second,  even  greater  accuracy  would  be  neces- 
sary. When  bulb  radiophone  transmitters  are  used,  the  filament  cur- 
rents and  reactions  on  the  oscillator  must  be  kept  quite  constant  else  there 
will  be  changes  in  the  emitted  frequency  even  in  this  case,  and  beat 
reception  will  not  be  feasible. 


Selectivity  vs.  Signal  Strength  209 

(c)  SELECTIVITY  IN  RECEPTION. 

There  is  a  fairly  sharp  conflict  between  the  requirement  of  loud 
signals  and  extreme  selectivity.  The  first  of  these  generally  requires 
sensitive  detectors  and  powerful  amplifiers  used  with  close  coupling  to 
the  antenna  system,  while  the  second  tends  in  the  opposite  directions. 
Nor  does  beat  reception  solve  this  problem  as  will  be  evident  below.  All 
that  can  be  said  is  that  a  rational  compromise  must  be  effected  in  every 
case,  this  to  be  determined  by  the  operating  conditions  in  the  neighbor- 
hood of  the  receiving  station.  Thus  the  amount  of  interference  in  the 
vicinity  of  the  receiver  is  an  extremely  important  factor  in  determining 
the  amount  of  power  required  at  the  transmitter  to  cover  the  desired 
distance.  This  is  a  factor  which  is  often  overlooked  in  the  design  of 
stations. 

There  is  also,  particularly  at  long  waves,  a  conflict  between  the  ex- 
treme antenna  persistence  necessary  for  adequate  selectivity  in  reception 
and  the  undesired  fly-wheel  effect  which  has  been  previously  mentioned. 
This,  again,  must  be  met  by  compromise. 

The  effect  of  modulation  on  selectivity  has  been  considered  on  page 
181. 

(d)  INTERFERENCE  WITH  RADIOPHONE  RECEPTION. 

Interference  from  spark  stations  disturbs  radiophone  reception  less 
than  might  be  expected,  partly  because  the  dots  and  dashes  constitute  a 
more  or  less  intermittent  disturbance  through  which  portions  of  the 
words  can  be  heard  and  partly  because  of  the  resulting  "assistance  of 
context"  effect.  Sustained  wave  station  interference  is,  however,  very 
serious  since  this"  causes  a  continuous  musical  note  by  the  beats  with  the 
incoming  radiophone  frequency  and  this  continuous  musical  note  cannot 
be  tuned  out  either  by  ordinary  or  beat  reception  being  a  physically 
present  phenomenon  caused  by  two  frequencies  external  to  the  receiving 
station.  In  the  neighborhood  of  a  large  arc  radio  telegraphic  station, 
this  may  become  a  very  grave  matter  particularly  if  compensation  waves 
are  used  by  the  arc  station  in  transmission.  In  this  latter  case,  there  will 
generally  be  produced  a  long  series  of  overtones  of  both  the  sending  and 
the  compensation  waves,  and  there  is  very  likely  to  be  continuous  beat 
interference.  The  Author  is  very  much  of  the  opinion  that  radiation  at 
non-useful  frequencies  should  not  be  permitted  since  the  growth  of  the 
radio  art  will  be  much  hampered  thereby.  Furthermore,  provision  should 
be  made  in  all  sustained  wave  stations  to  avoid  the  production  of  these 
series  of  overtones  (which,  it  may  be  mentioned,  are  frequently  not 
harmonics  but  fall  at  non-integral  multiples  of  the  main  and  useful 
frequency).  Furthermore,  bulb  beat  receivers  should  be  so  designed 
that  the  locally  generated  oscillations  are  without  overtones. 


210  Telephone  Receivers 

(e)  TELEPHONE  RECEIVERS. 

It  might  be  expected  that  there  would  be  no  great  difference  between 
the  various  telephone  receivers  used  in  radio  sets,  so  far  as  speech  recep- 
tion were  concerned,  but  this  is  far  from  being  the  case.  In  addition  to 
marked  differences  in  intrinsic  sensitiveness,  the  receivers  show  differences 
as  to  the  extent  to  which  they  distort  speech  and  the  relative  extent  to 
which  they  respond  to  the  sudden  shocks  caused  by  heavy  strays.  Gen- 
erally speaking,  the  receivers  with  diaphragms  of  moderate  thickness  give 
good  articulation,  moderate  sensitiveness,  no  inordinate  response  or 
''singing"  when  stray  impulses  are  received,  and  are  robust.  More 
sensitive  receivers  with  very  light  diaphragms  tend  to  give  "tinny" 
speech  and  more  than  proportionate  response  to  impulses. 

A  number  of  other  types  of  receivers  besides  the  usual  electromag- 
netic type  have  been  suggested.  Thus  Messrs.  Fessenden,  and,  later,  Ort 
and  Eieger  have  built  electrostatic  receivers.  These  are  nothing  more 
than  a  condenser  one  or  both  sets  of  plates  of  which  are  movable.  The 
electrostatic  forces  developed  as  the  difference  of  potential  between  the 
plates  changes  will  cause  minute  movements  of  the  plates  and  consequent 
sound.  Sometimes  an  auxiliary  potential  is  kept  constantly  on  the  plates 
and  they  are  under  considerable  tension,  this  being  found  to  increase  the 
sensitiveness  greatly.  Such  an  arrangement,  though  it  approaches  the 
usual  receiver  in  sensitiveness  is  not  particularly  convenient  and  has  not 
found  favor  in  the  commercial  radio  field. 

Mr.  Fessenden  has  further  developed  and  used  a  receiver  based  on 
alternating  current  repulsion  between  two  coils  of  wire  each  carrying  the 
same  current,  or  a  current  of  nearly  the  same  frequency.  The  construc- 
tion of  the  device  was  simple.  Two  flat  spirals  of  thin  wire  were  placed 
parallel  and  near  to  each  other,  and  the  incoming  current  passed  through 
both,  or  else  through  one  of  them  with  a  locally  generated  radio  frequency 
current  passing  through  the  other.  While  the  device  was  operative,  it 
did  not  find  favor  in  the  radio  field,  and  is  not  used  in  practice  at  present. 

(f)  RECEIVING  APPARATUS. 

The  first  receiver  we  shall  consider  is  that  shown  in  Figure  201.  It 
is  the  usual  audion  used  as  a  detector.  Incoming  radio  frequency  energy 
causes  radio  frequency  potential  differences  at  the  terminals  of  the 
secondary  tuning  condenser  Cx.  Consequently  alternating  current  tends 
to  flow  in  the  grid-to-filament  circuit,  C^C2GF.  However,  since  the  grid- 
to-filament  has  unidirectional  conductivity  only,  the  grid  gradually  accu- 
mulates a  larger  and  larger  negative  charge,  which  charge  cannot  escape 
through -Li  to  the  filament  because  of  the  grid  condenser  0,2.  In  conse- 
quence of  the  increasingly  negative  potential  of  the  grid,  the  current  in 


Audion  Detector  Receiver 


211 


FIGURE  201 — Normal  audion  receiver. 

the  plate  circuit  diminishes.  If  the  signals  cease,  the  grid  leakage 
(through  the  condenser  <72,  through  the  glass  supports  of  the  grid,  and 
because  of  any  residual  positive  ionisation  due  to  gas  molecules  in  the 
space  between  the  grid  and  filament)  will  speedily  bring  the  grid  poten- 
tial back  to  normal  and  the  plate  current  will  then  increase  to  its  usual 
value.  As  a  result  of  this  action,  variations  in  the  incoming  radio  fre- 
quency currents,  such  as  occur  in  radio  telephony,  will  be  approximately 
followed  by  changes  in  the  plate  current  of  the  audion.  A  supplementary 
resistance  may  be  shunted  across  the  grid  condenser  so  as  to  increase  grid 


Hflh 

B1 


FIGURE  202 — Armstrong  regenerative  circuit  for  radio 
frequency  amplification. 


212 


Audion  Regenerative  Amplification 


leakage  and  improve  the  fidelity  of  reproduction  of  speech  in  the  plate 
circuit.  This  will  generally  diminish  the  audion  sensitiveness.  The  re- 
sistance used  in  practice  for  this  purpose  are  pencil  lines,  graphite  rods, 
or  liquids  (e.  g.,  xylol),  and  have  values  ranging  from  a  few  thousand 
ohms  to  several  megohms.  In  addition,  high  vacuum  three-electrode 
tubes  can  be  used  as  detectors  by  virtue  of  the  curvature  of  the  plate 
current-grid  voltage  characteristic. 

As  explained  in  connection  with  Figure  79,  page  85,  Mr.  E.  H. 
Armstrong  has  devised  a  number  of  methods  of  using  the  audion  as  a 
regenerative  relay  by  coupling  the  plate  and  grid  circuits.  Such  an  ar- 
rangement adapted  for  telephonic  reception  and  giving  radio  frequency 
amplification  is  represented  in  Figure  202.  As  will  be  seen,  the  grid 


FIGURE  203 — Armstrong  regenerative  circuit  for  radio 
frequency  amplification  with  plate  circuit  tuning. 

circuit  L'C^L^  is  coupled  to  the  plate  circuit  by  means  of  the  inductive 
coupling  L'L".  Armstrong  has  found  in  bulbs  used  by  him  (high  vacuum 
bulbs)  that  the  regenerative  amplification  obtained  was  fifty-fold  in 
energy  or  about  7  times  in  audibility  (as  audibility  is  usually  defined, 
namely,  as  directly  proportional  to  the  current  through  the  telephone  re- 
ceivers). It  will  be  noted  that  the  telephone  T  is  shunted  by  the  con- 
denser C",  the  purpose  of  which  is  to  permit  the  passage  of  the  radio 
frequency  current  while  forcing  the  audio  frequency  currents  of  the 
signal  to  pass  through  the  receivers. 

An  improved  arrangement,  also  due  to  Armstrong,  is  shown  in 
Figure  203.  Here,  in  addition  to  the  regenerative  coupling  between  the 
plate  and  grid  circuits,  we  have  tuning  of  the  plate  circuit  by  means  of 


Audion  Regenerative  Amplification 


213 


FIGURE  204 — Armstrong  regenerative  circuit  for  radio 
frequency  amplification. 


the  inductance  L2  and  the  condenser  C".  As  before,  the  receivers  T  and 
the  plate  battery  B'  are  shunted  by  the  by-pass  condenser  C".  Another 
interesting  modification  is  given  in  Figure  204.  Here  the  coupling  is 
secured  by  means  of  the  large  inductance  L'  and  the  capacity  Cx.  The 
details  of  this  circuit  together  with  the  detailed  explanations  of  the 
various  circuits  here  outlined  and  similar  circuits  can  be  obtained  in  the 


FIGURE  205 — de  Forest  ultraudion  receiver. 


214 


de  Forest  "Ultraudion"  Receiver 


''Proceedings  of  The  Institute  of  Radio  Engineers,"  for  September,  1915. 
It  need  only  be  mentioned  here  that  it  is  recommended  that  the  induct- 
ances in  the  plate  and  grid  circuits  be  large  and  the  capacities  small. 

For  the  sake  of  completeness,  we  include  here  as  Figure  205  the 
de  Forest  ultraudion  circuit  which  has  previously  been  explained  in 
connection  with  Figure  86,  page  91.  The  modified  ultraudion  circuit 
having  grid  and  plate  circuit  coupling  by  means  of  the  so-called  ' '  tickler 
coils"  is  shown  and  explained  in  connection  with  Figure  87. 

The  actual  appearance  of  a  de  Forest  assembled  audion  and 
ultraudion  receiving  set  is  indicated  in  Figure  206.  The  tubular  audion 


FIGUEE  206 — de  Forest  Company  receiver,  1914. 

is  mounted  at  the  left  with  its  carbon  sector  potentiometer  (for  obtaining 
a  continuously  variable  plate  potential)  to  the  right  of  the  supporting 
socket.  The  bridging  condenser  and  the  stopping  condenser  (C"  and  C2 
respectively  of  Figure  205)  are  controlled  by  the  switches  below  the  bulb. 
The  three  top-row  knobs  control  an  antenna  loading  coil,  a  secondary 
loading  coil,  and  a  coupling  between  the  primary  (antenna)  circuit  and 
the  secondary  circuit.  The  two  lower  knobs  control  an  antenna  tuning 
condenser  and  the  secondary  circuit  tuning  condenser.  It  will  be  seen 
that  a  special  switch  is  used  in  connection  with  the  loading  coils  so  as  to 
avoid  dead  ends  when  using  only  a  portion  of  each  coil. 

The  general  appearance  of  the  de  Forest  audion  and  three  stage 
amplifier  is  shown  in  Figure  207.  The  lowest  bulb  is  the  detector,  the  re- 
mainder are  audio  frequency  amplifiers.  Each  has  its  own  filament 


Meissner  Receivers 


215 


current  rheostat  and  its  own  dry  cell  plate  battery  variable  in  steps  of  3 
volts.    The  telephone  can  be  plugged  in  at  any  stage  as  desired. 

In  Figure  208  is  represented  a  general  type  of  circuit  devised  by 
Dr.  Meissner  of  the  Telefunken  Company.  It  differs  from  the  preceding 
in  the  method  of  obtaining  plate  circuit  outputs.  Instead  of  inserting  the 
telephone  receivers  into  the  plate  circuit,  the  large  inductance  L.,  is 


FIGURE   207— de   Forest   audion   and   three 
stage  amplifier. 


placed  in  this  circuit,  and  the  alternating  potential  differences  appearing 
at  its  terminals  cause  currents  to  flow  in  the  tuned  circuit  L3C5  which  is 
coupled  t to  L2  by  the  condensers  C3  and  C4.  The  right  hand  bulb  serves 
as  a  detector  and  amplifier,  and  finally  delivers  audio  frequency  currents 
to  the  telephone  T.  Another  form  of  receiver  of  the  Telefunken  Company, 
devised  by  Count  von  Arco  and  Dr.  Meissner  is  represented  in  Figure  209 
It  will  be  seen  that  this  differs  from  Mr.  Armstrong's  circuit  of  Figure 


216 


Marconi  Company  Receivers 


FIGURE  208 — Telefunken  Company-Meissner  receiving  system. 

203  only  in  the  mode  in  which  the  plate  circuit  output  is  delivered  to  th< 
receivers. 

The  receiving  set  used  with  the  Marconi  Company's  radiophom 
transmitter  shown  in  Figure  153,  page  156,  and  described  in  conjunctioi 
therewith  is  indicated  in  Figure  210.  The  grid  circuit  is  coupled  directly 
to  the  antenna  circuit  through  a  portion  of  the  antenna  inductance  7 
and  the  inductance  L'.  The  grid  circuit  is  also  coupled  regenerativ( 
to  the  plate  circuit  through  the  coupling  between  L'  and  L".  The  plat< 
circuit  is  tuned  by  means  of  the  condenser  C'.  The  plate  battery  B  hai 
a  voltage  of  200  and  the  resistances  Rt  and  R2,  which  limit  the  pi  a  I 
current,  are  each  2,000  ohms.  The  battery  and  its  associated  resistance- 
are  shunted  by  the  condenser  C"  which  passes  the  amplified  radio  fre 


Lm  W*     , TT. 

H--wLw  r 


FIGURE    209 — Telefunken    Company-Arco-and-Meissner 
receiving  system. 


Bulbs  of  Western  Electric  Company 


217 


cy  current.  The  filament  of  the  bulb  is  lit  by  the  6-volt  battery 
nd  grounded  through  the  potentiometer  resistance  R'.  The  output 

plate  circuit  is  drawn  from  the  condenser  C'  across  which  is  placed 
usual  crystal  detector,  auxiliary  potential,  and  telephone  receiver 
)ination.  In  other  words,  the  system  shown  consists  of  a  regenerative 

frequency  amplifier  combined  with  an  ordinary  crystal  rectifying 
it  for  utilising  the  amplifier  output. 


FIGURE  210 — Marconi  Company  radiophone  receiver. 

Passing  to  the  work  of  the  Western  Electric  Company,  we  consider 
t  some  of  the  tubes  developed  by  the  engineers  of  that  company  and 
ir  method  of  construction.  One  type  of  tube,  due  to  Mr.  H.  J.  van 

Bijl,  is  shown  in  Figure  211.  Herein  the  objects  are  to  keep  the 
nes  of  the  grid  and  filament  close  together  (for  high  amplification) 
I  to  avoid  undue  tensions  on  the  filament.  As  will  be  seen  from  the 
er  portion  of  the  figure,  the  filament  is  threaded  to  and  fro  on 
flat  mica  support,  passing  alternately  from  one  side  of  the  mica  to 
other.  The  grid  and  its  supporting  frame  are  mounted  close  to  the 
sa,  and  are  preferably  arranged  as  shown  in  the  lower  portion  of  the 
ire,  that  is,  with  the  grid  wires  not  crossing  at  the  portions  of  the 
•a  where  the  small  vertical  portions  of  the  filament  are  exposed  on 
t  side.  In  another  form  of  tube,  due  to  Mr.  A.  McL.  Nicolson,  and 
resented  in  Figure  212,  it  is  attempted  to  secure  li efficient  control' ' 
twining  the  grid  wire  around  the  filament,  separating  them  only  by  a 
L-conductmg  or  dielectric  film.  Nickelous  oxid  is  recommended  for  the 
•pose.  In  the  form  shown  in  Figure  212,  the  grid  wires  1  are  coated 
h  nickelous  oxid,  and  around  them  are  twined  the  filament  wires  2. 
i  plates  3  are  situated  as  usual. 


218 


Manufacture  of  Western  Electric  Bulbs 


A  type  of  Western  Electric  Company  amplifier  or  "repeater"  tube 
is  shown  in  Figure  213.  This  type  is  due  to  Messrs.  A.  McL.  Nicolson 
and  E.  C.  Hull.  The  distinctive  feature  thereof  is  the  twisted  platinum 
filament  2,  which  is  coated  with  metallic  oxids.  It  is  made  by  dipping  a 
platinum  ribbon  having  a  width  of  say  0.3  mm.  (0.012  inch)  and  a  thick- 
ness of  0.05  mm.  (0.002  inch)  in  chromic  or  nitric  acid,  washing  it  in 
water,  and  then  in  a  strong  solution  of  ammonia.  After  this  thorough 
cleansing,  it  is  heated  to  incandescence  to  see  if  it  has  any  defects.  It 
may  then  be  dipped  in  a  trough  filled  with  dilute  strontium  hydroxid  and 
thereafter  dried  at  100°  C.  (212°  F.)  by  a  current  of  1.4  amperes.  After 


12' 

H 


FIGURE    211 — Western    Electric 
Company-van  der  Bijl  am- 
plifier tube,  1915. 


FIGURE    212 — Western    Electric 
Company-Nicolson    ampli- 
fier tube,  1914. 


four  such  coatings,  the  filament  is  heated  to  incandescence  for  a  few 
seconds  to  harden  the  oxid  film.  It  is  next  coated  with  barium  resinate 
melted  at  a  temperature  of  600°  C.  (1,100°  F.),  and  given  four  coats 
thereof  as  before  except  that  it  is  heated  for  a  few  seconds  to  incan- 
descence after  each  coat  or  two.  The  entire  process  thus  far  mentioned 
is  then  repeated,  thus  giving  four  sets  of  four  coats  of  the  oxid  or  resinate 
in  all.  The  filament  is  then  kept  at  incandescence  for  about  2  hours  at 
800°  C.  (1,470°  F.)  to  ignite  the  resinate.  The  resulting  film  of 
strontium  and  barium  oxids  on  the  filament  is  smooth  and  tough  and 


General  Electric  Company  Pliotron  Amplifier 


219 


FIGURE      214  —  General      Electric 

Company-White  small  pliotron 

amplifier. 


FIGURE     213  —  Western 

Electric  Company, 

Nicolson-and-Hull 

amplifier  tube, 

1914. 

gives  high  electron  emission  at  com- 
paratively low  temperatures,  thus 
tending  to  give  a  long  filament  life 
in  use.  Tubes  of  this  sort,  but  with 
a  grid  and  plate  at  each  side  of 
the  filament,  are  widely  used  by  the 
Company. 

One  type  of  receiver  used  by 
the  Western  Electric  Company  con- 
sist of  a  number  of  steps.  The  antenna  circuit  is  coupled  to  a  radio 
frequency  regenerative  amplifier,  much  like  that  shown  in  Figure  202  in 
most  respects  except  that  the  output  is  obtained  by  coupling  in  the  plate 
circuit  to  a  fairly  large  impedance  as  in  Figure  208.  The  next  circuit 
is  a  detector  circuit,  also  provided  with  regenerative  coupling.  The  out- 
put of  this  step  passes  into  a  two-step  audio  frequency  amplifier  with 
inductive  coupling  between  the  steps.  The  final  output  is  inductively 
coupled  to  a  balanced  receiver  for  reducing  the  relative  intensity  of 
strays,  and  devised  on  somewhat  the  same  general  lines  as  that  shown 
in  Figure  215  except  that  three-electrode  tubes  are  used. 

The  General  Electric  Company  has  constructed  a  number  of  differ- 
ent types  of  pliotron  amplifier  tubes,  one  type  of  which  intended  for 
relatively  small  outputs  is  shown  in  Figure  214.  The  grid  G  is  made 
of  very  fine  wire  wound  on  a  glass  frame.  Inside  the  grid  is  the  "V" 
or  "W"  shaped  filament  F.  The  plate  P  is  not  a  solid  plate  of  metal, 
but  consists  of  a  zig-zag  wire  supported  on  wire  supports  placed  appro- 


220 


Methods  of  Stray  Reduction 


priately  in  two  "  U "  shaped  glass  frames.  The  filament  leads  are  B  and 
(7,  the  plate  terminal  D,  and  the  grid  terminal  A.  The  whole  structure 
is  carefully  built  and  exhausted  to  an  extremely  high  vacuum  at  which 
'  *  pure  electron ' '  effects  are  obtained.  Under  these  conditions  it  has  been 
found  possible  to  obtain  extremely  high  audio  and  radio  frequency 
amplifications  without  using  regenerative  circuits  in  connection  with 


FIGURE  215 — Marconi  Company-Round  balanced  valve  receiver. 

the  bulb,  that  is,  without  any  other  coupling  between  grid  and  plate 
circuits  than  the  small  capacitive  coupling  which  necessarily  exists 
within  the  bulb. 

Mr.  Alexanderson  has  shown  several  methods  whereby  a  number  of 
such  tubes  may  be  used  in  cascade,  each  giving  radio  frequency  ampli- 
fication. It  is  claimed  that  the  selectivity  of  the  resulting  system  is 
high,  rising  in  geometric  proportion  to  the  number  of  steps. 


(g)   STRAYS. 

We  have  previously  considered  to  some  extent  "Stray  Interference 
in  Radio  Telephony, ' '  page  18. 

It  remains  to  consider  some  of  the  technical  expedients  at  present 
available  for  reducing  somewhat  the  disturbing  influence  of  strays.  The 
chief  of  these  are: 

(1)  Loose  coupling  between  the  antenna  and  receiver. 

(2)  Sharp  tuning  with  circuits  of  fairly  low  damping. 

(3)  Beat  reception   (which  is  sometimes  not  readily  applicable  to 
radio  telephony). 

(4)  Balanced  crystal  or  valve  detectors,  which  prevent  excessive 
crashes  of  sound  from  reaching  the  ear. 


Balanced  Valve  Stray  Reducer 


221 


(5)  Special  methods,  given  below. 

The  first  three  of  these  methods  are  commonly  known.  A  simple 
circuit  diagram  illustrating  the  balanced  valve  receiver  (as  due  to  Mr. 
H.  J.  Round  of  the  Marconi  Company  of  England)  is  given  in  Figure 
215.  Here  LC  is  the  secondary  of  an  ordinary  receiver,  and  T  a  tele- 
phone receiver.  The  two  hot-electrode  rectifiers  (Fleming  valves)  Vl 
and  V2  are  connected  as  shown.  The  batteries  Bl  and  B2  serve  not  only 
to  light  the  filaments  through  the  appropriate  controlling  resistances 
rx  and  r2  but  also  to  provide  a  supplementary  potential  difference  in  the 
plate  circuits  through  the  potentiometer  control  resistances  R^  and  R2. 
It  is  well  known  that  the  curve  connecting  excitation  (that  is,  incoming 
signal  current)  and  response  (that  is,  rectified  current)  depends,  in 


—  EXCITATION  — 


FIGURE    216 — Valve    characteristics    with 
different  auxiliary  potentials. 

these  valves,  on  the  supplementary  potential  in  the  plate  circuit.  Hence 
we  arrange  that  one  of  these  valves  shall  have  a  favorable  value  of  this 
potential,  giving  it  high  sensitiveness  for  weak  signals.  This  will  be 
valve  V2,  and  its  sensitiveness  curve  is  shown  in  Figure  216.  The  other 
valve,  Fj,  is  run  with  a  low  supplementary  potential,  so  that  its  sensi- 
tiveness for  weak  signals  is  very  low.  For  extremely  loud  signals,  how- 
ever (because  of  the  current  saturation  effect)  its  response  is  no  less 
than  that  of  V,2.  It  will  be  noticed  that  the  valves  V1  and  V2  are  con- 
nected in  opposition  or  differentially  so  far  as  the  receiver  T  is  con- 
cerned. Hence  weak  signals  will  be  readable  since  T7t  will  not  neutralise 
F2  in  this  case.  Strong  crashes  due  to  strays  will  affect  both  valves 
equally,  and  hence  will  not  be  heard  in  T. 

An  alternative  scheme,  proposed  by  Dr.  L.  W.  Austin,  is  to  connect 
a  silicon-arsenic  detector  direct  between  antenna  and  ground  as  a  shunt 
to  the  primary  of  the  inductive  receiving  coupler.  This  detector  is 
claimed  not  to  affect  weak  signals,  but  to  become  conductive  for  ex- 


222 


Dieckmann  Cage  Stray  Reducer 


tremely  powerful  disturbances,  thus  shunting  them  to  ground  and  pro- 
tecting the  ear  sensitiveness  of  the  receiving  operator. 

A  Dieckmann  electrostatic  shield  for  a  flat  top  antenna  is  shown 
in  Figure  217.  The  purpose  of  such  a  shield  is  to  prevent  the  electro- 
static field  of  the  earth  or  of  the  atmosphere  from  reaching  the  antenna, 
by  an  action  similar  to  that  of  a  Faraday  cage.  At  the  same  time,  the 
shield  must  be  so  arranged  that  the  incoming  electromagnetic  waves 
can  pass  through  readily,  as  in  the  case  of  a  Hertzian  polarizing  parallel- 


/ 


FIGURE  217 — Dieckmann  shielding  cage  for  stray  re< 
duction. 

wire  screen.  In  Figure  21-7,  A  is  the  actual  antenna  with  its  down  lead 
D.  The  actual  shielding  wires  are  T  and  those  parallel  to  it.  The  wires 
R  and  those  parallel  to  it  are  merely  equalising  connections,  and  include 
inserted  resistances  so  that  the  entire  shielding  system  is  aperiodic ;  that 
is,  incapable  of  being  set  into  resonant  oscillation  by  the  incoming 
energy.  This  is  an  obvious  necessity.  The  shielding  system  is  grounded 
at  U  through  a  large  inductance  or  resistance.  In  practice,  Dieckmann 
found  that  the  reception  was  louder  when  the  antenna  A  was  shielded 
than  when  it  was  not  (because  of  increased  capacity  when  the  shield 
was  present).  Naturally,  this  type  of  shield  protects  strictly  against 
"static"  but  not  against  all  strays,  since  distant  electromagnetic  waves 
from  terrestrial  sources  can  pass  through  it.  In  practice,  however,  Dieck- 
mann found  it  to  be  of  marked  assistance  very  frequently,  a  fact  since 
verified  by  other  careful  investigators. 

The  Author  has  suggested  in  the  past  the  use  of  a  completely 
covered  antenna  wire,  the  insulator  being  smooth  and  non-hygroscopic, 
thus  preventing  charged  air  and  water  particles  from  giving  their 


Classification  of  Stray  Intensity  223 

charges  by  contact  to  the  antenna,  with  the  resulting  disturbance  of 
reception.  Such  a  method  should  be  of  assistance  at  times,  though  it 
would  naturally  not  be  nearly  so  efficient  a  protection  as  a  Dieckmann 
shield,  since  it  would  fail  entirely  to  guard  the  antenna  against  aperiodic 
sudden  changes  in  the  earth's  electrostatic  field. 

We  shall  now  consider  some  further  points  in  connection  with 
strays  and  radio  telephony.  To  begin  with,  it  must  be  noted  that  with 
the  modern  sensitive  receivers  (e.  g.,  the  regenerative  vacuum  tube 
receivers),  heavy  strays  do  much  m^re  damage  than  to  act  merely  as 
incidental  noises.  They  break  up  the  incoming  sustained  wave  trains 
so  far  as  the  receiving  system  is  concerned  and  thus  prevent  resonance 
phenomena  in  circuits  of  small  (or  even  zero  or  negative)  damping  from 
being  fully  utilised.  In  addition,  some  types  of  detectors  (e.  g.,  sensitive 
crystals  or  gas-containing  bulbs)  may  be  "paralysed"  by  heavy  strays 
and  take  some  little  time  to  regain  their  sensitiveness.  Even  very 
high  vacuum  tubes  may  show  this  effect,  since  a  very  powerful  stray 
impulse  may  charge  the  grid  negatively  to  such  an  extent  that  the  plate 
current  will  be  practically  cut  off  until  the  grid  charge  escapes  by  the 
normal  leakage.  Then,  too,  the  ear  will  be  so  shocked  by  heavy  bursts  of 
strays  that  it  will  take  some  little  time  to  regain  its  normal  sensitiveness. 

The  Author  has  found,  in  connection  with  some  tests  in  radio  tele- 
phony over  fairly  considerable  distances,  that  really  good  reception 
requires  that  the  signal  audibility  shall  be  3  times  that  of  the  strays, 
and  that  the  strays  shall  not  occur  continuously  even  then  but  inter- 
mittently, and  not  more  frequently  than  say  once  or  twice  per  second. 
Fair  reception  can  still  be  accomplished  even  if  the  (intermittent) 
strays  are  2  times  as  strong  as  the  signal.  Reception  becomes  difficult 
if  the  strays  are  5  times  as  strong  as  the  signal,  and  almost  impossible 
if  the  ratio  is  greater,  particularly  if  the  strays  are  continuous. 

Dr.  C.  J.  de  Groot  has  given  in  the  "Proceedings  of  The  Institute 
of  Radio  Engineers"  for  April,  1917,  a  classification  of  the  strength  of 
tropical  strays  (with  a  crystal  detector  and  normal  Telefunken  receiver) 
and  the  signal  strength  necessary  for  telegraphic  communication  through 
such  strays.  The  number  of  the  class  is  on  an  arbitrary  scale. 

0.  No  disturbance.     (Signal  strength  would  be  a  few  times  audibility.) 

1.  Weak  strays.    Requiring  a  signal  of  10  times  audibility. 

2.  Medium  strays.    Requiring  a  signal  of  20  to  30  times  audibility. 

3.  Strong  strays.    Requiring  a  signal  of  60  times  audibility. 

4.  Heavy  (or  very  heavy)   strays.     Requiring  a  signal  of  250  to  500 
times  audibility. 


224 


Electrical  Classification  of  Strays 


5.     Overwhelming  strays  or  thunderstorms.    This  case  occurred  only  for 
an  hour  or  two  during  the  very  worst  days  in  the  least  favorable 
part  of  the  year.     Reception  under  such  conditions  is  not  possible. 
Dr.   de  Groot  showed  that  musical  spark  signals  could  be  read 
through  strays  that  had  (at  least  intermittently)  an  audibility  nearly 
70  times  as  great  as  that  of  the  signal  and  an  audibility  at  almost  all 
times  of  10  or  20  times  that  of  the  signal.     This  he  imputes  to  the  re- 
markable  selective    sensitiveness   of    the    ear   to   musical   tones.      This 
advantage  is  not  present  to  the  same  extent  in  radio  telephony. 

Dr.  de  Groot  further  classified  strays  into  three  classes  electrically 
and  gave  the  details  of  the  production,  nature,  and  elimination  of  each 
class. 


FIGURE   218 — de   Groot   audio   frequency   compensation 
method  for  the  elimination  of  periodic  strays. 


Type  1.  These  are  strays  originating  in  nearby  thunderstorms, 
and  they  have  only  a  short  range.  They  are  found  to  be  of  periodic 
character  (i.  e.,  decadent  wave  trains  of  definite  period  and  decrement). 
They  are  heard  in  the  receiver  as  loud,  widely  separated  clicks,  and  may 
be  eliminated  by  audio  or  radio  frequency  compensation.  The  arrange- 
ment given  by  de  Groot  for  this  purpose  is  shown  in  Figure  218  and 
is  explained  by  him  as  follows:  "Two  receiving  antennas,  Llt  L2  of  the 
same  shape  and  dimensions  were  installed  near  enough  together  (10  or 
20  meters  or  30  to  60  feet  apart)  to  make  them  respond  in  the  same  way 
to  strays.  (For  the  aperiodic  disturbances  this  distance  could  be  easily 
increased,  but  for  periodic  disturbances  the  distance  of  separation  must 
be  small  compared  to  the  wave  length  of  the  strays,  in  order  to  get  the 


Compensation  Method  of  Stray  Reduction  225 

induced  e.m.f.'s  in  phase).  On  the  other  hand  the  antennas  must  be 
placed  sufficiently  far  apart  so  that  the  signals  set  up  in  the  one  which 
is  made  aperiodic  (L2)  shall  not  cause  currents  in  the  tuned  antenna 
(LJ.  One  of  the  antennas,  Z/1?  is  tuned  to  the  incoming  signal  and 
coupled  to  the  detector  circuit  D^  in  the  ordinary  way.  The  detector 
I>t  will  rectify  signals  as  well  as  strays  and  send  the  rectified  current 
into  the  telephones ;  or,  as  in  the  case  of  the  figure,  into  the  differential 
transformer  Tr.  The  antenna  L2  is  tuned  either  to  the  same,  or  prefer- 
ably to  a  longer  wave-length,  thus  making  it  less  sensitive  to  the  signals 
and  more  sensitive  to  the  long  wave  strays.  The  detector  D2  is  switched 
directly  into  this  antenna,  thus  making  it  aperiodic  or  nearly  so.  This 
arrangement  makes  it  almost  impossible  to  receive  any  distant  signals  on 
the  antenna  L2,  but  loud  signals  on  wave-lengths  different  from  those  to 
which  Ll  is  tuned  and  strays  give  a  response  that  is  nearly  as  loud  as 
can  be  obtained  on  the  tuned  antenna  Llf  The  rectified  current  is  sent 
to  the  same  telephone  mentioned  before;  or,  as  in  the  figure,  to  the 
differential  transformer  Tr.  However,  this  second  current  from  the 
aperiodic  antenna  L2  is  arranged  to  act  in  the  opposite  direction  from 
that  of  Dj.  The  telephone  T  is  either  connected  in  series  with  D^  and 
J>2 ;  or,  as  in  the  figure,  in  a  third  winding  of  the  differential  trans- 
former and  in  series  with  the  condenser  C  to  permit  tuning  to  the  spark 
frequency.  Since  D2  does  not  respond  to  distant  signals,  there  will  be 
heard  in  the  telephones  the  signals  from  Dv  only,  whereas  the  strays 
rectified  by  Dv  and  Z>2  tend  to  compensate.  By  varying  the  coupling  K19 
this  compensation  may  be  made  complete. ' '  Dr.  de  Groot  mentions  that 
the  detectors  must  both  have  the  same  characteristic  and  states  that  car- 
borundum crystals  with  suitable  auxiliary  potential  meet  the  require- 
ments. The  theory  here  given  yielded  very  promising  results  when 
tested.  For  further  details  of  this  method,  the  reader  is  referred  to 
the  original  article. 

Type  2.  These  strays  are  associated  with  low-lying  (electrically 
charged)  rain  clouds  and  are  of  very  short  range.  Electrically,  they 
are  found  to  be  intermittent  uni-directional  currents  due  to  actual  dis- 
charges to  or  from  the  antenna.  They  are  audible  as  a  constant  hissing 
sound,  and  are  eliminable  by  the  Dieckmann  electrostatic  shield  shown 
and  explained  in  connection  with  Figure  217. 

Type  3.  These  are  most  common  or  night  strays  and  cause  most 
of  the  interference  with  reception.  They  are  believed  to  originate  in  the 
Heaviside  layer  or  conducting  portion  of  the  upper  atmosphere  when 
this  is  subjected  to  the  cosmic  bombardment  of  small  particles  and 
comets.  The  range  (with  the  receiver  used)  was  several  hundred  miles, 


.226 


Range  in  Radio  Telephony 


Range 

Km.  Mies 


MM- 


3000- 


2000- 


1000 


&>6     7     8      9    *">    //     /*     jy     /f 


i6     /r 


FIGURE  219 — Yearly  increase  in  range  in  radio  telephony. 


Range  in  Radio  Telephony  227 

and  these  strays  gave  a  continuous  rattling  noise.  They  were  success- 
fully eliminated  by  means  of  the  Dieckmann  cage  of  Figure  217. 

Much  valuable  information  on  the  daily  and  seasonal  variation  of 
strays  is  given  in  Dr.  de  Groot  's  paper.  The  reader  is  also  referred  to  the 
Author's  discussion  on  that  paper  for  a  further  explanation  of  the 
Dieckmann  cage. 

The  first  approximation  to  the  ratio  of  heavy  summer  strays  to  light 
winter  strays  is  probably  between  100-to-l  to  1,000-to-l  or  even  more. 

(h)    RANGE  IN   RADIO   TELEPHONY. 

As  has  been  previously  stated,  the  effective  range  of  a  radiophone 
transmitter  depends  on  the  loudness  of  strays  at  the  receiving  station; 
and  consequently  any  method  of  reducing  strays  will  increase  the 
effective  power  of  the  transmitter  in  just  that  proportion. 

In  1908,  Mr.  Fessenden,  as  the  result  of  some  rather  elaborate 
analysis,  reached  the  conclusion  that  the  amount  of  power  required  to 
cover  a  given  range  radiophonically  was  from  5  to  15  times  as  great  as 
that  required  to  cover  it  radio  telegraphically.  It  is  certain,  how- 
ever, that  some  of  the  reasoning  there  given  is  not  valid,  and  par- 
ticularly that  dealing  with  the  greater  amount  of  power  required  in 
radio  telephony  because  of  the  relatively  small  amplitude  of  the  higher 
harmonics  in  the  human  voice.  It  seems  much  more  likely  that  about 
the  same  amount  of  power  is  required  to  cover  a  given  distance  by  means 
of  either  system  of  communication  excluding  beat  reception  from  con- 
sideration. 

We  have  compiled  from  the  material  presented  in  this  volume  e 
maximum  distance  covered  each  year  radiophonically.  The  data  is 
given  in  the  chart  of  Figure  219.  It  will  be  noticed  that,  practically 
speaking,  radio  telephony  began  in  1906  when  a  range  of  160  miles 
(250  km.)  was  covered.  It  must  be  mentioned,  however,  that  Fessenden 
had  transmitted  speech  by  a  radio-frequent  spark  method  a  distance  of 
1  mile  (1.6  km.)  as  early  as  1900.  The  range  increased  fairly  steadily 
at  the  rate  of  about  60  miles  (100  km.)  per  year  until  1915,  when  it  took 
a  sudden  jump  to  the  extreme  range  of  5,100  miles  (8,000  km.).  The 
dashed  curve  A  shows  this  material  clearly.  We  have,  however,  endea- 
vored to  distinguish  between  distance  actually  covered  as  an  extreme 
achievement  and  the  distance  which  could  have  been  reliably  covered 
with  the  apparatus  available  at  any  given  time.  The  second  curve  B 
gives  the  range  of  probable  reliable  communication  at  any  given  year. 
It  will  be  seen  that  this  range  has  risen  from  about  40  miles  (65  km.) 
in  1906  to  about  500  miles  (800  km.)  in  1917.  In  fact,  it  is  believed 
that  with  the  equipment  the  performance  oscillograms  of  which  are  given 
in  Figure  200,  page  202  (that  is,  the  Alexanderson  alternator-magnetic 


228 


Relation  of  Range  and  Power 


Km.  flii/ef 


voo 


345 
Afftfnn*.  Kilo  if/off s 


FIGURE  220 — Relation  between  range  and  antenna  power  in  radio  telephony. 

amplifier  combination  controlling  35  kilowatts)  reliable  overland  tele- 
phony over  1,000  miles  (1,600  km.)  or  more  could  be  accomplished. 
We  desire  to  emphasize  particularly  the  distinction  between  "extreme 
range"  and  "range  of  reliable  communication."  It  is  to  be  regretted 
that  we  have  had  so  much  of  the  former  type  of  achievement  in  radio 
telephony  and  so  very  little  of  the  latter.  In  view  of  the  large  ratio 
between  them,  it  is  felt  that  only  the  latter  type  is  of  any  real  interest, 
and  that  it  only  should  be  stressed  hereafter. 

In  Figure  220  are  given  two  curves  connecting  the  range  in  radio 
telephony  with  the  antenna  kilowatts  (not  transmitter  input).  These 
curves  are  also  based  on  the  data  given  in  this  book.  The  upper  curve  A 
gives  "extreme  ranges,"  and  shows  the  following  interesting  facts. 
With  an  antenna  power  of  only  about  0.5  kilowatt,  300  miles  (500  km.) 
can  sometimes,  though  rarely,  be  covered.  With  1  kilowatt,  this  rises  to 


Reliable  vs.  Occasional  Range  229 

600  miles  (1,000  km.).  At  10  kilowatts,  it  rises  to  5,000  miles,  (8,000 
km.).  The  " range  of  reliable  communication,"  given  in  Figure  220, 
curve  B  is  very  different.  It  will  be  seen  that  1  antenna  kilowatt  will 
cover  not  over  about  150  miles  (250  km.)  overland  at  the  most  desirable 
wave-length.  For  about  10  antenna  kilowatts,  this  range  rises  to  500 
miles  (800  km.).  The  difference  is  very  significant  between  curves  A 
and  B,  and  these  curves  cannot  be  brought  closer  together  until  the 
matter  of  stray  elimination  is  settled.  Even  then,  daylight  and  summer 
absorption  of  the  electromagnetic  waves  will  prevent  the  curves  from 
being  identical. 


CHAPTER  X. 

10.  RADIOPHONE  TRAFFIC  AND  ITS  REGULATION,  (a)  DUPLEX 
OPERATION;  METHOD  OF  MARCONI;  METHOD  OF  FESSENDEN; 
METHOD  OF  CARSON,  (b)  SHIP-TO-SHORE  RADIO  TELEPHONY. 
(c)  LONG  DISTANCE  RADIO  TELEPHONY;  RATES;  RADIO 
TELEPHONY  VERSUS  RAPID  RADIO  TELEGRAPHY,  (d)  FUTURE 
DEVELOPMENT  OF  RADIO  TELEPHONY. 

10.  RADIOPHONE  TRAFFIC  AND  ITS  REGULATION, 
(a)  DUPLEX  OPERATION. 

Any  one  who  has  compared  normal  telephone  conversation  with  the 
irritating  substitute  provided  by  an  ordinary  speaking  tube  will  realize 
the  full  necessity  for  duplex  operation,  i.  e.,  simultaneous  transmission 
and  reception  without  the  necessity  for  handling  any  switches  or  other 
devices  when  the  speaker  desires  to  listen,  or  vice  versa.  Experience 
teaches  that  sending-to-receiving  switches  lead  to  endless  annoyance  and 
confusion  unless  there  is  some  skilled  person  standing  next  to  the  user 
of  the  radiophone  to  explain  in  detail  how  the  switch  is  handled  and  to 
rectify  errors  of  manipulation.  While  this  latter  procedure  may  be 
possible  with  a  ship  radiophone  station,  where  the  passenger  desiring  to 
telephone  to  land  may  put  himself  under  the  temporary  guidance  and 
instruction  of  the  skilled  radiophone  operator,  it  would  not  be  feasible 
on  land  since  any  system  of  land  radio  telephony  must  provide  that  calls 
may  originate  at  any  wire  line  subscriber's  station,  whether  at  his  home 
or  place  of  business.  Since  the  land  subscriber  cannot,  therefore,  come 
to  the  radiophone  station,  there  will  be  no  opportunity  to  give  him  the 
necessary  personal  supervision  and  instruction. 

A  practical  system  of  duplex  radio  communication  (applicable  to  tele- 
phony) has  been  worked  out  by  Mr.  Guglielmo  Marconi.  The  arrangement 
at  the  duplex  sending  and  receiving  station  is  shown  in  Figure  221.  The 
transmitting  antenna  A  is  a  long  horizontal  antenna,  and  directive  (at 
any  rate,  for  moderate  distances  and  in  reception).  The  main  receiving 
antenna,  Alf  is  directive  and  parallel  to  the  first.  Both  of  these  there- 
fore point  to  the  distant  station.  In  addition  to  the  main  receiving 
antenna  Aly  there  is  a  balancing  antenna  A,  so  placed  as  to  receive 
strongly  from  the  transmitting  antenna  A  but  very  little  from  the 
distant  station.  The  distance  CD  in  practice  is  anywhere  from  25  to  50 

230 


Marconi  Duplex  System 


231 


miles  (40  to  80  km.).  A  telegraph  or,  in  our  case,  telephone  line  con- 
nects the  stations.  The  receiver  at  BD  is  so  arranged  that  it  is  coupled 
to  the  coils  in  both  antennas  A^  and  A2  differentially.  By  suitable 
adjustment,  it  then  becomes  possible  to  cut  out  completely  the  signal 
from  A  while  retaining  the  signal  from  the  distant  transmitter  almost 
undiminished.  Thus  simultaneous  transmission  and  reception  become 
possible. 


1= 

s      +* 


FIGUBE  221 — Marconi  duplex  station. 


Another  method,  due  to  Mr.  Fessenden,  is  indicated  in  principle 
only  in  Figure  222.  The  four  batteries  A,  B,  C,  and  D  are  connected  in 
series  assisting  as  indicated.  Resistances  R^  and  R2  are  inserted  as  shown. 
Under  these  conditions,  the  points  X  and  Y  will  be  found  to  be  at  the 
same  potential,  and  a  sensitive  galvanometer  connected  across  them  will 
show  no  deflection.  Translated  into  the  corresponding  radio  equivalent, 
the  actual  arrangement  is  shown  in  Figure  223.  The  radio  frequency 
alternator  /  (in  series  with  the  microphone  M  OF  other  controlling  device) 
sends  current  through  the  coils  H,  G,  E,  and  F.  There  are  thus  induced 
in  the  coils  C,  D,  A,  and  B  assisting  currents.  The  resistance  R±  of  Fig- 
ure 222  is  replaced  by  the  artificial  antenna  R±  of  Figure  223,  and  the 
R2  of  Figure  222  by  the  actual  antenna  of  Figure  223.  The  four  coils 
in  the  antenna  circuit  correspond  to  the  four  batteries.  As  will  be  seen, 
the  points  X  and  T  in  Figure  223  are  at  the  same  potential  so  far  as  the 
alternator  is  concerned,  and  a  receiving  set  m?y  be  connected  across 
them  when  the  arrangement  is  properly  adjusted.  This  receiver  will 
respond  (to  some  extent)  to  incoming  signals.  This  entire  arrangement, 


232 


Fessenden  Duplex  System 


FIGURE  222 — Principle  of  Fesseuden  duplex  system. 

while  very  ingenious,  suffers  from  a  number  of  practical  disadvantages. 
To  begin  with,  the  exact  balance  is  very  difficult  to  secure  and  even 
more  difficult  to  maintain  because  of  changes  in  antenna  and  ground 
conditions.  Furthermore,  the  points  X  and  Y  while  at  equal  potential, 
are  far  above  ground  potential,  and  consequently  capacity  currents  will 
flow  from  the  receiving  set  to  ground,  disturbing  the  balance  and  giving 


FIGURE  223 — Fessenden  duplex  system  for  radio  telephony. 

false  signals.  In  addition,  at  least  half  of  the  available  energy  will  be 
lost  in  the  artificial  antenna  R^  and  more  than  half  of  the  incoming  signal 
energy  will  be  lost  in  all  cases. 

A  somewhat  similar  arrangement,  invented  by  Mr.  J.  H.  Carson  and 


Carson  Duplex  System 


233 


assigned  to  the  American  Telephone  and  Telegraph  Company,  is  shown 
in  Figure  224.  It  will  be  seen  that  the  secondary  L'  of  the  output  trans- 
former of  the  radio  frequency  alternator  Q  has  two  equal  parallel  load 
circuits.  One  of  these  is  the  path  Clf  Llf  and  the  artificial  antenna  Alf 
while  the  other  is  the  exa  „  y  similar  path  C2,  L,2,  and  the  actual  antenna 
A2.  The  receiving  set  is  coupled  differentially  to  the  two  paths,  and  will 


FIGURE  224 — American  Telephone  and  Telegraph  Company-Carson  sys- 
tem for  duplex   radio   telephony. 


therefore  respond  only  to  incoming  signals.  It  contains  the  loop  circuit 
L5C3  intended  to  cut  down  any  unbalanced  energy  at  the  transmitting 
wave  length  which  may  chance  to  get  into  the  receiver.  This  arrangement 
is  subject  to  exactly  the  same  defects  as  those  pointed  out  in  connection 
with  Mr.  Fessenden's  above. 

Another  type  of  system  intended  to  accomplish  the  same  results  as 
actual  duplex  working  has  been  worked  out  by  Dr.  de  Forest  and  along 
independent  lines  by  some  of  the  engineers  of  the  General  Electric  Com- 
pany. This  consists  of  a  voice-controlled  relay  which  changes  over  the  set 
from  receiving  to  transmitting  when  speech  is  begun.  A  sluggish  contact 
device  (e.  g.,  mercury  in  a  capillary  tube)  is  closed  by  the  voice  vibration 
or  the  exhaled  breath  and  the  set  is  then  thrown,  through  the  action  of 
more  robust  relays,  into  the  transmitting  setting.  The  controlling  device 


234 


Voice-Controlled  Duplex  Sets 


is  usually  located  in  or  v^ery  near  to  the  microphone  transmitter,  uther 
systems  along  similar  lines  have  been  proposed,  all  depending  on  changes 
caused  by  the  voice  or  voice  currents,  but  there  is  no  data  available  for 
publication  as  the  extent  to  which  they  are  capable  of  practical  applica- 
tion. 

We  will  not  discuss  here  such  methods  of  duplex  working  as  the 
commutator  method,  wherein  the  antenna  is  thrown  in  rapid  succession 


Lindhursf- 


"Curalo* 


FIGURE  225 — Typical  sliip-to-sliore  radiophone  system. 

from  the  transmitter  to  the  receiver  and  back.  While  these  may  be 
suitable  for  telegraphy,  they  are  obviously  unsuited  for  telephony  because 
of  their  almost  certain  destruction  of  the  quality  of  the  speech.  Even  if 
the  commutation  is  done  above  audio  frequency  (which,  in  itself,  is 
hardly  very  practical),  the  method  would  be  open  to  grave  objections. 


Ship-to-Shore  Radiophone  Traffic  235 

(b)  SHIP-TO-SHORE    RADIO    TELEPHONY. 

The  most  casual  consideration  of  the  question  of  ship-to-shore  radio 
telephony  forces  us  to  accept  the  conclusion  that  this  vastly  important 
system  is  dependent  for  its  full  development  on  the  voluntary  or  enforced 
co-operation  of  the  wire  telephone  companies.  It  is  obvious  that  it  is  not 
possible  to  have  a  fairly  large  radiophone  set  at  the  home  or  office  of 
every  one  who  may  at  some  time  or  other  desire  to  speak  with  a  person 
on  board  a  ship,  but  that  the  land  end  of  the  conversation  must  be  car- 
ried on  from  a  large  commercial  radiophone  station  which  automatically 
relays  the  speech  out  from  the  wire  lines.  Similarly  the  incoming  speech 
from  the  ship  must  be  received  at  the  same  or  another  radiophone  station 
and  there  relayed  back  to  the  wire  lines  and  thence  to  the  subscriber. 
The  procedure  may  be  made  clear  from  Figure  225.  We  will  suppose 
that  Mr.  Frank  Jones,  whose  wire  telephone  number  in  New  York  City 
is  Dyckman  386,  desires  to  radiophone  to  Mr.  William  Smith  on  board 
the  steamship  "Curalo,"  some  500  miles  (800  km.)  at  sea.  Let  us  sup- 
pose that  a  duplex  radiophone  system  (using,  for  example,  the  twin 
station  Marconi  plan  given  in  Figure  221)  is  installed  at  the  two  towns 
near  New  York  which  have  the  assumed  names  of  Clairview  and  Lind- 
hurst.  We  shall  take  the  transmitting  station  to  be  Clairview.  At  Clair- 
view there  will  be  a  usual  telephone  connection,  itself  connected  to  a 
private  telephone  line  between  Clairview  and  Lindhurst.  Lindhurst  is 
the  receiving  station  (with  its  balancing  antenna  as  indicated  in  Figure 
221).  At  Clairview,  the  incoming  telephone  line  has  inserted  in  it  or 
across  it  the  input  side  of  a  line  amplifier  which  increases  the  energy  of 
the  speech  current  to  the  point  of  enabling  control  of  the  radiophone 
transmitter  at  Clairview.  The  wire  line  terminating  in  Lindhurst  is 
there  connected  to  the  output  side  of  an  amplifier  which  increases  the 
intensity  of  the  incoming  radiophone  signals  to  the  point  where  they  can 
be  sent  through  Clairview  to  the  calling  or  called  subscriber's  station. 
On  board  the  "Curalo"  we  have  a  moderately  skilled  operator,  who 
among  his  other  duties,  listens  for  distress  calls.  Either  the  operator  or 
one  of  the  ship 's  engineers  keeps  the  ship's  radiophone  set  in  order.  We 
shall  assume  that  the  set  on  board  the  ship  is  not  equipped  for  duplex 
work,  though  it  is  probable  that  eventually  even  the  ship  sets  will  be 
duplex.  The  change-over  will  be  assumed  to  be  accomplished  by  pressing 
down  a  push  button  when  talking  and  releasing  it  when  receiving,  the 
push  button  circuit  actuating  some  form  of  relay  control  switch  which 
transfer  from  sending  to  receiving  or  vice  versa. 

We  shall  now  proceed  to  give  in  detail  the  conversation  between 
practically  all  the  parties  involved  in  the  above  call  between  Messrs. 
Jones  and  Smith.  It  is  understood  that  this  will  be  somewhat  imagina- 


236  Ship-to-Shore  Radiophone  Procedure 

tive  and  subject  to  revision  in  details,  though  it  is  probably  a  fairly 
faithful  impression  of  the  actual  procedure : 

MR.  JONES  (on  his  wire  telephone)  :     Radio  long  distance,  please. 

OPERATOR  (AT  DYCKMAN  CENTRAL)  :  One  minute,  please.  (She 
connects  his  line  to  the  Clairview  Radio  Station  line.  The  internal  proce- 
dure at  the  central  or  centrals  is  here  omitted.) 

OPERATOR  (AT  CLAIRVIEW)  :     Radio  long  distance  speaking. 

MR.  JONES:  I  wish  to  speak  to  Mr,  William  Smith  on  board  the 
steamship  ' '  Curalo. ' ' 

OPERATOR  (AT  CLAIRVIEW)  :  Mr.  William  Smith  on  board  the 
' '  Curalo. ' '  What  is  your  number  ? 

MR.  JONES  :  Dyckman  386,  Mr.  Frank  Jones,  the  subscriber,  speak- 
ing. 

OPERATOR  (AT  CLAIRVIEW)  :  Thank  you.  Hang  your  receiver  on 
the  hook.  I  will  call  you  as  soon  as  your  connection  is  ready. 


OPERATOR  (AT  CLAIRVIEW,  talking  out  on  the  radiophone)  :  Hello, 
Curalo.  Hello,  Curalo.  Hello,  Curalo.  New  York  calling. 

OPERATOR  (ON  "CURALO")  :     Hello,  New  York.     "Curalo"  talking. 

OPERATOR  (AT  CLAIRVIEW)  :  I  want  Mr.  William  Smith.  Mr.  Frank 
Jones  of  New  York  calling. 

OPERATOR  (ON  "CURALO")  :  Mr.  Frank  Jones  calling  Mr.  William 
Smith  ? 

OPERATOR  (AT  CLAIRVIEW)  :    Yes,  please. 

OPERATOR  (ON  "CURALO")  :  Hold  the  air,  please.  I  will  call  Mr. 
Smith.  (The  operator  on  the  *  *  Curalo ' '  then  calls  Mr.  Smith  to  the  radio 
cabin,  and  explains  to  him  how  to  change  from  talking  to  listening  by 
releasing  the  controlling  push  button.  The  method  being  learned,  he 
resumes  as  follows)  : 

OPERATOR  (ON  " CURALO")  :  Hello,  New  York.  Mr.  Smith  is  ready 
for  you  now. 

OPERATOR  (AT  CLAIRVIEW,  on  wire  line)  :  Hello,  Dyckman.  Clair- 
view calling.  Give  me  386  again,  please. 

OPERATOR  (AT  DYCKMAN)  :     386? 

OPERATOR  (AT  CLAIRVIEW)  :     Yes,  please. 

MR.  JONES  (at  his  wire  telephone)  :  Hello.  This  is  Dyckman,  386. 
Mr.  Frank  Jones  speaking. 

OPERATOR  (AT  CLAIRVIEW)  :  Mr.  Smith  is  ready  for  you  now.  t  Go 
ahead  please.  (The  operator  at  Clairview  here  closes  the  necessary 
amplifier  circuits  and  takes  a  supervisory  role  only.) 

M*.  JONES:     Hello,  Mr.  Smith.     Jones  calling. 


Radiophone  Traffic  Regulation  237 

MR.  SMITH:  Hello,  Jones.  This  is  certainly  a  pleasant  surprise. 
How  are 

It  will  be  seen  from  a  careful  reading  of  the  above  that  the  pro- 
cedure is  no  more  elaborate  than  for  any  ordinary  "particular  person" 
long  distance  call.  Furthermore,  so  far  as  the  calling  and  called  persons 
are  concerned,  there  is  no  more  difficulty  or  confusion  than  in  any  ordin- 
ary call.  To  verify  this,  the  reader  is  urged  to  re-read  Mr.  Jones'  and 
Mr.  Smith's  remarks  above. 

It  need  hardly  be  said  that  the  system  of  charging  for  a  radiophone 
conversation  would  be  on  the  basis  of  time  and  not  on  the  basis  of  words 
as  in  telegraphy.  As  to  the  extent  of  the  charge,  this  might  depend  on 
several  factors.  •  To  begin  with,  a  somewhat  deferred  service  correspond- 
ing roughly  to  "day  letters"  or  even  to  "night  letters"  in  ordinary 
telegraphy  seems  feasible  at  a  considerably  lower  rate  per  minute.  The 
season  of  the  year  and  the  distance  over  which  the  call  has  been  made 
might  also  be  factors  of  the  situation,  though  to  what  extent  only  prac- 
tical experience  and  the  development  of  the  art  can  determine. 

There  is  one  direction  in  which  radio  legislation  properly  conceived 
can  greatly  assist  the  radiophone  field.  This  is  by  providing  a  system 
whereby  every  ship  and  its  corresponding  shore  station  have  available  not 
one  or  two,  but  a  considerable  number  of  wave  lengths.  These  wave 
lengths,  which  should  be  designated  by  letters  or  numbers  for  the  sake 
of  brevity,  would  all  be  available  for  communication  except  those  that 
were  in  actual  use  near  the  receiving  station.  That  is,  the  receiving  sta- 
tion, after  listening  for  a  momentj  would  dictate  to  the  transmitting 
station  the  suitable  wave  length  for  communication  without  interference. 
Naturally  all  calling  would  be  done  on  a  common  wave  length  which  might 
be,  for  example,  the  present-day  600  meter  wave.  This  system  of  a 
multiplicity  of  legal  wave  lengths  and  the  choice  of  one  of  them  for 
communication  in  accordance  with  traffic  conditions  at  the  receiving 
station  has  great  possibilities,  and  should  be  carefully  considered  for 
future  action  by  the  International  Radio  Convention  and  the  Govern- 
ments of  the  world. 

One  further  interesting  possibility  of  radio  telephony  on  board  ship 
may  be  mentioned.  A  simple  phonograph  recording  and  reproducing 
device  run  by  a  small  motor  might  be  provided  so  that,  in  case  the  pas- 
sengers and  crews  are  forced  to  desert  the  ship  after  a  serious  accident, 
the  phonograph  can  continue  to-  repeat  into  the  radiophone  transmitter 
the  necessary  call  for  help,  the  name  of  the  ship,  its  location,  the  type  of 
accident,  and  the  action  taken  by  the  passengers  and  crew.  This  would, 
to  some  degree  at  least,  relieve  the  operator  from  the  heroic,  but  fre- 
quently fatal,  stand  which  up  to  the  present  he  has  always  taken  •*  With 


238  Long  Distance  Radiophone  Traffic 

this  simple  device  installed,  he  has  at  least  the  same  chance  of  rescue  as 
the  other  officers  of  the  ship. 

(c)  LONG  DISTANCE  RADIO  TELEPHONY. 

This  also  must  be  accomplished  with  the  co-operation  of  the  wire 
telephone  companies,  and  it  is  to  be  hoped  that  they  will  adopt  a  broad 
policy  of  co-operation  with  radio  telephony  in  this  regard.  Since  a  large 
portion  of  the  long  distance  radio  telephony  will  be  trans-oceanic  (in 
which  case  wire  telephony  cannot  come  into  competition),  such  an  atti- 
tude on  the  part  of  the  wire  telephone  companies  will  involve  no  in- 
ordinate sacrifice,  and  will,  indeed,  probably  add  very  largely  to  the  long 
distance  land  wire  line  tolls. 

We  shall  give  here  also  the  sample  procedure  of  a  long  distance 
radiophone  call  over  the  5,500  miles  (9,000  km.)  between  New  York 
City  and  Buenos  Aires.  We  shall  suppose  that  Mr.  Frank  Jones  of 
Dyckman  386  is  calling  Mr.  J.  Desigante  of  Ciudad  762  in  Buenos  Aires. 
We  shall  assume  now  that  Clairview  and  Lindhurst  have  the  same  func- 
tions as  in  the  case  described  previously  except  that  they  are  naturally 
,  provided  with  a  much  more  powerful  transmitter  and  a  suitable  receiving 
set.  At  Buenos  Aires,  the  transmitting  station  is  at  the  (assumed)  town 
of  Sol  del  Plata,  and  the  receiver  at  the  (assumed)  town  of  Parina.  The 
wire  line  connections,  line  amplifiers,  and  auxiliary  apparatus  are  like 
those  at  Clairview  and  Lindhurst.  Speech  from  Mr.  Jones  to  Mr. 
Desigante  travels  over  the  following  route: 

Mr.  Jones  at  Dyckman  386 — Dyckman  central — (possible  intermedi- 
ate centrals  not  here  considered)— Clairview — (by  radio)  Parina — (by 
wire)  Sol  del  Plata — (possible  intermediate  centrals  not  here  considered) 
— Ciudad  central — Mr.  Desigante  at  Ciudad  762. 

Speech  from  Mr.  Desigante  to  Mr.  Jones  travels  as  follows : 

Mr.  Desigante  at  Ciudad  762— Ciudad  central— (possible  inter- 
mediate centrals  not  here  considered) — Sol  del  Plata — (by  radio)  Lind- 
hurst—  (by  wire)  Clairview  (possible  intermediate  centrals  not  here  con- 
sidered)— Dyckman  central — Mr.  Jones  at  Dyckman  386. 

These  paths  are  shown  clearly  in  Figure  226.  The  detailed  dialogue 
between  all  parties  involved  is  here  given.  In  addition,  before  each  re- 
mark we  give  the  elapsed  time  in  minutes  and  seconds  very  roughly 
estimated : 

0.00 — MR.  JONES  (on  his  wire  telephone)  :  Radio  long  distance, 
please. 

0.05 — OPERATOR  (AT  DYCKMAN  CENTRAL)  :  One  minute,  please. 
(She  connects  his  line  to  the  Clairview  Radio  Station  line.  The  internal 
procedure  at  the  central  or  centrals  is  here  omitted.) 

0.25 — OPERATOR  (AT  CLAIRVIEW)  :     Radio  long  distance  speaking. 


Long  Distance  Radiophone  Procedure 


239 


0.30 — MB.  JONES:  I  wish  to  speak  to  Buenos  Aires.  A  particular 
person  call  for  Mr.  J.  Desigante,  D-e-s-i-g-a-n-t-e,  whose  number  is 
Ciudad  762. 

0.45 — OPERATOR  (AT  CLAIRVIEW)  :  Buenos  Aires,  Mr.  J.  Desigante, 
D-e-s-i-g-a-n-t-e,  of  Ciudad  762.  What  is  your  number? 

1,00 — MR.  JONES:  Dyckman  386,  Mr.  Frank  Jones,  the  subscriber, 
speaking. 

1,05 — OPERATOR  (AT  CLAIRVIEW)  :  Thank  you.  Hang  your  receiver 
on  the  hook.  I  will  call  you  as  soon  as  your  connection  is  ready. 


C/airview 


Lindhurst 


386 


Dyckman 
Central 


5500 
Miles 
$000  tin) 


BUENOS  AIPE5 


SolcfelPlafa 


Parma          s«b3C£ib*L 

-^ 

CiudadCenM 


FIGURE  226 — Typical  duplex  long  distance  radiophone 
system. 


240  Long  Distance  Radiophone  Procedure 

1.20 — OPERATOR  (AT  CLAIRVIEW,  talking  out  on  the  radiophone)  : 
Hello,  Buenos  Aires.  Hello,  Buenos  Aires.  Hello,  Buenos  Aires.  New 
York,  calling. 

1.45 — OPERATOR  (AT  SOL  DEL  PLATA,  receiving  through  Parina)  : 
Hello,  New  York.  Buenos  Aires  speaking. 

1.50 — OPERATOR  (AT  CLAIRVIEW)  :  I  want  Ciudad  762,  Mr. 
J.  Desigante,  D-e-s-i-g-a-n-t-e.  Mr.  Frank  Jones  calling. 

2.15 — OPERATOR  (AT  SOL  DEL  PLATA)  :  Ciudad  762,  Mr.  J.  De- 
sigante, D-e-s-i-g-a-n-t-e.  Mr.  Frank  Jones  calling.  Hold  the  air,  please. 
(Speaking  on  the  wire  line.)  Hello,  Ciudad.  Sol  del  Plata  calling. 

2.35 — OPERATOR  (AT  CIUDAD)  (The  internal  procedure  at  the  central 
or  centrals  is  here  omitted)  :  Hello,  Sol  del  Plata.  Ciudad  speaking. 

2.40 — OPERATOR  (AT  SOL  DEL  PLATA)  :     Ciudad  762,  please. 

2.42— OPERATOR  (AT  CIUDAD)  :  762? 

2.45 — OPERATOR  (AT  SOL  DEL  PLATA)  :     Yes,  please. 

2.55— MR.  DESIGANTE  (on  his  wire  telephone)  :  Hello,  this  is  Ciudad 
762.  Mr.  J.  Desigante  speaking. 

3.00 — OPERATOR  (AT  SOL  DEL  PLATA)  :  Mr.  Frank  Jones  of  New 
York  wishes  to  speak  to  you.  Hold  the  wire,  please.  (By  radiophone)  : 
Hello,  Clairview.  Ciudad  762  is  ready  for  you  now. 

3.20 — OPERATOR  (AT  CLAIRVIEW)  :  Thank  you.  Hold  the  air, 
please.  (By  wire  telephone)  :  Hello,  Dyckman.  Clairview  calling. 
Give  me  386  again,  please. 

3.30— OPERATOR  (AT  DYCKMAN)  :     386? 

3.33 — OPERATOR  (AT  CLAIRVIEW)  :     Yes,  please. 

3.50 — MR.  JONES  (on  his  wire  telephone)  :  Hello,  this  is  Dyckman 
386.  Mr.  Frank  Jones  speaking. 

3.53 — OPERATOR  (AT  CLAIRVIEW)  :  Mr.  Desigante  is  ready  now.  Go 
ahead,  please.  (The  operator  at  Clairview  here  closes  the  necessary 
amplifier  circuits  and  takes  a  supervisory  role  only.) 

3.56 — MR.  JONES  :     Hello,  Mr.  Desigante.     Jones  speaking. 

4.00 — MR.  DESIGANTE  :     Hello,  Mr.  Jones.     Desigante  speaking. " 

4.01 — MR.  JONES:  About  that  shipment  number  1167  of  April  18th 
on  the  ' '  Curalo, ' '  I  wanted  to  ask  whether  .  .  .  . 


Future  Radiophone  Developments  241 

As  stated  before,  the  charges  on  such  telephone  service  might  well 
take  account  of  the  time  of  day  and  of  the  season  of  the  year. 

There  will  be  an  interesting  competition  between  very  high  speed 
telegraphy  (possibly  with  automatic  recording  and  transcribing  ap- 
paratus) and  radio  telephony  in  connection  with  the  normal  transaction 
of  business.  It  is  too  early  to  venture  any  predictions  regarding  the  re- 
sults of  such  competition.  However,  for  personal  communications  there 
can  be  no  doubt  as  to  which  form  of  communication  will  be  preferred. 

(d)  FUTURE  DEVELOPMENT  OF  RADIO  TELEPHONY. 

Now  that  the  need  for  radio  telephony  is  well  recognized,  we  may 
confidently  expect  a  very  rapid  development.  Once  a  public  demand  is 
created,  the  technical  advances  required  to  satisfy  that  need  must  shortly 
fellow. 

Some  interesting  possibilities  as  to  universal  communication  may  be 
considered.  So  far  as  portable  transmitters  are  concerned,  it  is  unlikely, 
for  some  time  to  come  that  a  man  will  be  able  to  carry  a  radiophone  set 
capable  of  communicating  more  than  a  few  miles.  Some  new  motive 
force,  the  apparatus  for  producing  which  has  a  very  small  weight  per 
kilowatt  delivered,  must  first  be  discovered.  So  far  as  reception  is  con- 
cerned, however,  very  sensitive  and  light  receiving  apparatus,  capable  of 
receiving  messages  from  hundreds  (or  even  thousands)  of  miles  is 
imaginable.  So  that  it  should  become  ultimately  possible  to  keep  in 
immediate  touch  with  the  traveling  individual  regardless  of  his  motion 
or  temporary  location.  A  great  field  of  usefulness  is  thus  opened  to 
development. 

The  linking  of  the  wire  telephone  and  radiophone  systems  of  a 
country  will  go  far  toward  making  it  possible  for  travelers  to  keep  in 
touch  with  their  homes  and  business  at  all  times,  and  for  the  people  of 
one  nation  to  know  the  people  of  far  distant  nations  in  a  close  and 
intimate  fashion.  By  the  use  of  a  deferred  or  night  radiophone  service 
(analogous  to  the  day  letter  or  night  letter  of  the  wire  telegraph  com- 
panies), reasonably  inexpensive  communication  of  this  type  should  be- 
come feasible  since  such  service  might  be  rendered  at  times  of  light  load 
and  would  tend  to  maintain  the  steady  usefulness  of  the  station.  As  is 
well  known,  stations  are  most  efficiently  operated  when  the  load  is 
nearly  atways  full  and  constant.  Plant  efficiency  requires,  therefore, 
that  some  sort  of  premium  be  put  on  utilization  of  the  plant  facilities 
at  times  of  normally  light  load. 

In  conclusion,  it  may  be  stated  that  it  is  certain  that  radio  telephony, 
properly  fostered  by  the  Governments  of  the  world,  must  become  ever 
more  useful  to  humanity.  From  ship  and  shore  stations,  from  aeroplane 


/ 


242  Future  Radiophone  Developments 


and  ground,  from  trains  and  depots,  over  forests  and  deserts,  across 
oceans  and  continents  will  pass  the  spoken  word  of  man.  We  may  justly 
paraphrase  President  Elliot's  splendid  eulogy  of  another  type  of  com- 
munication. His  words  apply  with  multiplied  force  to  the  radiophone  of 
the  future.  We  may  rightly  term  this  instrument  for  speeding  the  voice 
of  man  across  space  as : — 


CARRIER  OF  NEWS  AND  KNOWLEDGE. 

INSTRUMENT  OF  TRADE  AND  INDUSTRY. 

PROTECTOR  OF  LIFE  AT  SEA. 


MESSENGER  OF  SYMPATHY  AND  LOVE. 

SERVANT  OF  PARTED  FRIENDS. 

CONSOLER  OF  THE  LONELY. 


BOND  OF  THE  SCATTERED  FAMILY. 
ENLARGER  OF  THE  COMMON  LIFE. 


PROMOTER  OF  MUTUAL  ACQUAINTANCE. 
OP  PEACE  AND  GOOD  WILL  AMONG  MEN  AND  NATIONS. 


INDEX 


All  references  to  individuals,  companies,  equipment,  circuits,  or  radio 
stations  are  fully  listed  in  this  index.  With  the  exceptions  of  the  names  of 
companies,  all  topics  will  be  listed  in  general  under  the  NOTJtf  to  which  refer- 
ence  is  made.  The  numbers  correspond  to  pages  in  the  text.  The  following 
abbreviations  are  used:  r.f. — radio  frequency;  a,f.— audio  frequency;  r.t— radio 
telephony;  w.t. — wire  telephony. 

Arc,  Danish  Poulsen  Company,  30 

,  Dubilier,  48,  49 

,  equivalent  resistance  of,  22-25 

,  Federal  Telegraph  Company,  34 

— ,  field,  26,  37 

,  Fuller  circuit  for  increasing  effi- 
ciency, 26,  27 

,  hydrocarbon  atmosphere,  26,  40 

41,  56,  57,  65 
— ,  Lorenz  Company,  28 
— ,  Moretti,  70,  72 
— ,  Poulsen,  21-37,  66,  99,  131,  169 

,  self-regulating,  28,  63,  65 

— ,  Telefunken  Company,  37-39 
— ,  Telephone     Manufacturing     Cor- 
poration, 29,  30,  33 

,  theory  of  action,  25,  26 

Arco,  G.  von,  87,  104,  111,  215 

Arcs,  21-43 

Arlington,  Virginia   (station),  34,  168, 

Armstrong,  E.  H.,  85-87,  92,  207,  212 
Audion,    see    also    "Dynatron,    Relay 
(electron),    Pliodynatron,    Pliotron, 
Tubes    (vacuum)",   72,   82,   207,   210, 
211,  214 
Austin,  L.  W.,  221 


AUROPLANE-TO-GROUND,  R.  T.,  5, 
52,  58,  162,  163 

Aldene,  New  Jersey  (station),  157 
Alexanderson,  E.  F.  W.,  14,  15,  104,  116- 

126,  177,  183,  192-203,  220,  227 
Alternators,  r.f.,  103-126 

• ,  r.f.,  Alexanderson,       104, 

116-126,  177,  227 

— ,  r.f.,  Alexanderson,     char- 
acteristics of,  193-195 
— ,  r.f.,  Alexanderson,  "gyro" 
type,  123,  124 

- — — ,  r.f.,  Alexanderson,    triple 

frequency,  125,  126 

• ,  r.f.,  Arco,  104 

,  r.f.,  constructional     diffi- 
culties, 103,  104,  107-109 

• ,  r.f.,.  Goldschmidt,  104-110 

,  r.f.,  inductor,  114-126 

,  r.f.,  Telefunken          Com- 

pany-Arco,  114-116 
American    Telephone    and    Telegraph 

Company,  233 
Amplification,  non-linear,  15-17 

,  with  magnetic  amplifier, 

202,  203 
Amplifiers,  audion,  214,  215 

,  dynatron,  100 

,  Lieben  tube,  88 

,  magnetic,  15,  16,  124,  126, 

183,  192-203,  228 

• ,  magnetic,     characteristics 

of,  197-203 

— ,  magnetic,  construction  of, 

195,  196 

,  pliotron,  219,  220 

— ,  vacuum  tubes,  84,  85 
Amplifier,  circuits   Alexanderson,  220 
de  Forest,  163,  164 
Heising,  94-96,  167, 

168 

Meissner,  215,  216 
Round,  159,  217 
Western      Electric 

Company,  210 
Anderle,  F.,  30 
Anode,  in  dynatron,  98,  99 
Antenna,  balancing,  230 
Antennas,  13,  14,  205-207 
Arc,  Chaffee,  45,  46,  55,  56,  57,  71 
— ,  Colin  and  Jeance,  39-43,  135 


BECCO  DI  VELA,  SARDINIA  (STA- 
TION), 35 

Bell,  Chichester,  151 
Berlin,  Germany  (station),  39,  155 
Bethenod,  J.,  71 

Brant  Rock,   Massachusetts    (station), 
119,  122,  126,  139,  140 

GAGE,  DIECKMANN,  222,  227 
Cage,  Faraday,  222 
Calling,  selective,  62,  158 
Carnarvon,  Wales  (station),  74,  75 
Carson,  J.  H.,  232 
Cento  Celle,  Italy  (station),  72 
Chaffee,  E.  Leon,  45,  46,  55-61 
Chambers,  F.  J.,  149 
Changers,  frequency,  104 

,  frequency,      ferromagnetic, 

110-114,  188-192 

Characteristics,  of  vacuum  tubes,  83 
Charge,  space,  79 
Chokes,  r.f.,  Kiihn  system,  187,  188 

,  r.f.,  Telefunken  system,  196 

Circuit,  "fly-wheel,"  28 


243 


244 


Index 


Cohen,  Louis,  201 

Colin,  V.,  39-43,  135 

College  of  the  City  of  New  York  (sta- 
tion), 124,  126 

Colpitts,  E.  H.,  94,  166 

Compagnie  Generate  de  Radiotel- 
egraphie,  42 

Context,  assistance  by,  19,  20,  209 

Control,  modulation,  see  "Modulation, 
control" 

Coolidge,  78 

Coupling,  internal,  in  pliotrons,  178, 
179 

Current,  alternating,  used  with  vac- 
uum tubes,  170-173,  175 

Currents,  electron,  see  "Currents,  ther- 
mionic" 

Currents,  thermionic,  76-82 

,  thermionic  and  lighting 

combined  80,  81,  170,  171 

Cutting,  Fulton,  56,  58 

DARIEN,    PANAMA  CANAL   ZONE 
(STATION),  34 
de  Forest,  Lee,  14,  66-69,  82,  89-91,  134, 

214 

de  Forest  Radio  Telephone  and  Tele- 
graph Company,  159-166 
de  Gr^ot,  C.  J.,  223-227 
Delaware,  Lackawanna,  and  Western 

Railroad  (stations),  69 
Detector,  audion,  72,  82,  207,  210,  211, 
214 

• ,  crystal,  35,  42,  61,  64,  72,  216 

,  magnetic,  35 

Dieckmann,  M.,  222,  227 
Distortion,  antenna  persistency,  13, 14, 
206,  207 

ferromagnetic,  14,  15 

inductive,  13 

inertia  type,  12,  13 

microphone,  14 

non-linear,  15-17 

—    of  speech,  12-17,  36 

Distress,  calls  by  r.t.,  237,  238 

Ditcham,  W.  T.,  60,  62,  63,  136 

Doubler,  frequency,  Telefunken  Com- 
pany, 111-114  - 

Dubilier,  W.,  47-50,  141 

Duddell,  W.,  21 

Duplex,  r.t,  230-234 

,  r.t,  Carson  system,  232,  233 

,  r.t.,    de    Forest    system,    233, 

234 

,  r.t.,  Fessenden    system,     231, 

232 

— ,  r.t.,  General     Electric     Com- 
pany system,  233 

,  r.t.,  Marconi  system,  230,  231, 

235 

Dushman,  S.,  77,  80 

Dynatron,  see  also  "Audion,  Pliodyna- 
tron,  Pliotron,  Relay  (electron), 
Tubes  (vacuum),"  97-102,  175,  176 


EGNER,  C.,  36,  144,  146 
Eilvese,    German     (station),    34, 
107,  109 
Emission,  of  electrons,  77 

,  secondary,  of  electrons,  97- 

99 

Epstein,  111 
Esbjerg,  Denmark  (station),  27,  36,  147 

FACTOR,  OF  SAFETY,  IN  R.  T.,  19 
Federal  Telegraph  Company,  34 
Fessenden,  R.  A.,  46,  47,  117,  126,  135, 

137-141,  210,  227,  231-233 
Filaments,    in    vacuum    tubes,    oxid- 

coated,  82,  88 
Fleming,  J.  A.,  78 
Forte  Spurio,  Sicily  (station),  36 
Franklin,  W.,  89,  90 
Frequency,  inverse  charge,  46,  55,  61, 

71 
Fuller,  L.  F.,  26 

GAP,    AIR,    IN    R.    F.    ALTERNA- 
TORS, 122 
Gap,  Chaffee,  56,  57 

— ,  de  Forest,  tungsten,  G7,  68 

,  Ditcham,  60,  61 

,  Dubilier,  48,  49 

,  Hanscom,  65,  66 

,  Lepel,  53 

,  Lorenz  Company-Scheller,  52 

,  Moretti,  70 

,  rotary  high  speed,  47 

,  rotary  high  speed,  Fessenden,  73, 

74 

,  rotary  high  speed,  Marconi,     73, 

74 

,  Ruhmer,  47 

,  trigger,  Marconi,  75 

,  T.  Y.  K.,  62,  63 

General  Electric  Company,   (Schenec- 

tady,  New  York)   77,  81,  92,  93,  97, 

100,    101,   104,   116-126,   170-180,   183, 

192-203,  219,  220 
Glow,    blue,    in    gas-containing   tubes, 

82,  93,  155,  156 
Goldschmidt,  Robert,  72,  147 
Goldschmidt,  Rudolf,  104-109,  110,  136, 

137 

Grid,  in  vacuum  tubes,  82,  83,  93 
,  of  pliodynatron,  102 

•*       ' ; 

HANSCOM,  W.  W.,  65,  66 
Harfleur,  France  (station),  54 
Heaviside,  O.,  225 
Heising,  R.,  95,  167,  168 
Hogan,  J.  L.,  Jr.,  119 
Holmstrom,  J.  G.,  36,  144-146 
Honolulu,  Hawaii  (station),  168 
Hull,  A.  W.,  96-100 
Hull,  E.  C.,  218 


Index 


245 


INTERFERENCE,   IN  R.  T.  RECEP- 
TION,    BY     SUSTAINED     WAVE 
STATIONS,  209 
lonisation,  positive,  in  gas-containing 

tubes,  82 

Iron,  properties  of  at,  r.f.,  110-114,  184- 
186 

JAMAICA,  NEW  YORK  (STATION), 
126,  140 
Jeance,  M.,  39-43,  135 

KANN,  192 
Kenotron,  see  also  "Valve,  Flem- 
ing," 78,  98,  99,  170-175 
Kitamura,  M.,  62-65 
Kiihn,  L.,  183 

T  AEKEN,  BELGIUM  (STATION),  72, 
I-/      147 

Langmuir,  I.,  81,  83,  171 

La  Spezzia,  Italy  (station),  72 

Layer,  Heaviside,  225 

Leak,   grid,   in  vacuum   tube   circuits, 

91,   160,   211,   212 
Lepel,  E.  von,  53,  54 
Letchworth,  England  (station),  61 
Lieben,  E.  von,  82,  88,  155 
Lightning,  224,  225 
Limitation,  temperature,  of  thermionic 

currents,  78,  79 
Limitation,  space  charge,  of  thermionic 

currents,  79 
Logwood,  C.  V.,  159 
Lorenz  Company,  Berlin,  28,  135 
Los  Angeles,  California  (station),  34 
Lyngby,  Denmark  (station),  27,  36,  147 

MADDALENA,    SARDINIA     (STA- 
TION), 35,  72 

Majorana,  Q.,  35-37,  151,  152 
Marconi,  G.,  73-75,  230 
Marconi  Company  of  America,  157 
Marconi  Company  of  England,  89,  90, 

155-160,  216,  217,  221 
Mare  Island,  California  (station),  168 
Marion,  Massachusetts  (station),  74 
Marzi,  J.  B.,  72,  147 
Meissner,  A.,  87,  88,  111,  154,  155,  215 
Messina,  Italy  (station),  72 
Mettray,  France  (station),  42 
Microphone,  33,  128-135 

,  Chamber's  liquid,  149 

— ,  Dubilier,  141,  143 
— ,  Egner-Holmstrom,         36, 
144-146 

,  heating,  133,  138,  144,  145, 

146,  148 

— ,  high  current,  137-152 
— ,  hydraulic,  36,  71 
— ,  hydrogen  atmosphere  for, 
146 


Microphone,  Majorana's     liquid,      151, 

152 

— ,  Marzi,  147-149 
— ,  multiple,  27,  30,  31,  40,  67 

135-137,  183,  186 
— ,  Telephone  Manufacturing 

Corporation,  143,  144 
— ,  Vanni's  liquid,  149-151 
Microphones,  in  parallel,  136,  137,  186 
Mines-to-surface,  r.t,  5 
Modulation,     absorption    system,    vac- 
uum tube,  178-180 
— ,  amplitude,  9,  10 
— ,  classification    of   systems, 

132,  180,  181,  203,  204 
— ,  Colpitts  system,  167 
— ,  "complete,"  128 
— ,  composite,  12,  28,  39 

—  ,  condenser  transmitter,  141 
— ,  control,  127-204 

— ,  control         characteristic, 
127-131 

— ,  degree  of  control,  128-130 

— ,  ferromagnetic  control  sys- 
tems, 182-203 

— ,  General      Electric      Com- 
pany-White systems,  173 

— ,  grid  control,  128,  153-180 

— ,  high  current  microphone, 
137-152,  203 

— ,  Kiihn  system,  182-192 

— ,  magnetic      amplifier,     15, 
183,  204 

— ,  Marconi    Company-Round 
system,  156-160 

— ,  multiple  microphone,  135- 

137 
— ,    ordinary  microphone,  128, 

130,  131,  132-135,  203 

—  ,  "over",  15     . 

—  ,  pliodynatron,  Hull  system, 

176,  177 

—  ,  stability  of  control  in,  130, 

131,  134,  153,  154,  167 
— ,  vacuum  tube  control,  153- 

180 

—  ,  wave  length  change,  11 
Monofon  Company,  Stockholm,  146 
Monte   Mario,    Rome,    Italy    (station), 

35,  36 

Moretti,  70 

"Multitone,"   system  .of   Lorenz   Com- 
pany, 51,  52 

NATIONAL     ELECTRIC     SIGNAL- 
ING   COMPANY,    117,    119,    120, 
126,  137-141 
Nauen,  Germany  (station),  19,  155,  168, 

192 

News,  distribution  of,  by  r.t,  166 
Nicolson,  A.  McL.,  96,  217,  218 
Northampton,  England  (station),  61 


246 


Index 


OILING,    SYSTEM    OF,    IN   ALEX- 
ANDERSON    R.    F.    ALTERNA- 
TOR, 122 
Ort,  Carl,  210 
Oscillators,  vacuum  tube,  85-102 

— ,  -  —  ,  Arco  -  Meis- 

sner,  87 

,  —  — ,  Armstrong 

circuits,  86, 
212-214 

— ,  -  —  ,  Colpitt's  cir- 

cuit, 93,  94 

— ,  -  — ,  controlled 

p  1  iodyna- 
tron,  Hull 
circuit,  102 

— — ,  -  — ,de  Forest 

circuit,  90- 
92,  159,  214 

— ,  -  —  ,  dy  n  atron, 

Hull   cir- 
cuit, 100 
— ,  -  —  ,  Franklin 

circuit,  89 
— ,  -  —  ,  Meissner,87, 

154,   155 

— ,  -  —  ,  plate  cir- 

cuit tuning, 
86,  92 
— ,  —  —  ,  pliotron, 

171-175 

— ,  —  ,  Round  cir- 
cuit, 215, 
216 

Oscillion,  see  also  "Audion,  Dynatron, 
Pliodynatron,  Pliotron,  Relay  (elec- 
tron), Tube  (vacuum),"  92,  159,  161 
Over-modulation,  15 

PALERMO,   ITALY    (STATION),   72 
Paris,    France    (station),    42,   72, 

168 

Patents,  7 
Philadelphia,    Pennsylvania    (station), 

157,  158 

Pickard,  G.  W.,  61 
Pierce,  G.  W.,  55 

Pittsfield,  Massachusetts  (station),  180 
Plate,  in  vacuum  tubes,  77,  93 
Pliodynatron,  102,  176,  177 
Pliotron,  see  also  "Audion,  Dynatron, 

Pliodynatron,       Relay        (electron), 

Tube     (vacuum),"    92,     93,     170-175, 

178-180,  203,  219,  220 
Plymouth,     Massachusetts      (station), 

139,  140 

Ponza,  Italy   (station),  35,  72 
Porto  d'Anzio,  Italy  (station),  35 
Poulsen,  Valdemar,  14,  21,  26,  27,  66, 

134,  147 
Proceedings  of  the  Institute  of  Radio 

Engineers,  81,  86,  171,  179,  214,  223 


RADIATION,  AT  A.  F.,  FOR  R.  T.5 
8,   9 

Radiation,  at  r.f.,  for  r.t,  9-12 
Railroad,  r.t.,  see  "Train,  r.t." 
Range,   data  on,  27,  30,  31,  33,   34-36, 
39,  46,  49,  59,  60,  61,  66,  68,  69,  72, 
109,  124,  126,  139,  140,  147,  149,  151, 
152,  155,  157,  158,  161,  165,  166,  168, 
174,   175,   177,    180,    192,    227-229 
Range,  occasional     vs.     reliable,     168, 
228,  229 

,  r.t.  vs.  radio  telegraphy,  227 

Rating,  of  r.t,  transmitters,  131,  132 
Receivers,  r.t,  210-220,  224,  225 

— ,  r.t,  aperiodic        secondary, 

14,  27,  28 

— ,  r.t,  balanced      crystal      or 
valve,    220,    221,    224,    225 
— ,  r.t.,  selectivity  of,   208,   209 
— ,  telephone,  12,  .13,  210 
— ,  telephone,  a.c.       repulsion, 

210 

— ,  telephone,  electrostatic,  210 
Reception,  beat,  69,  75,  207,  208,  220 

,  in  r.t,  10,  11,  207-227 

Rectifiers,  necessity  for  in  r.t,  10,  11 
Regeneration,  in  vacuum  tube  circuits, 

86,  92,  212 

Regional,  r.t.,  arctic,  3 
— ,  r.t.,  desert,  3 

Regulation,  legal,  of  r.t.,  18,  59,  237 
Relay,  r.t.,  sending-to-receiving,  voice- 
controlled,  233,  234 
— ,  telephone,  Brown,  62 
— ,  telephone,  Dubilier,  48,  141-143 
— ,  telephone,  Fessenden,  137-140 
— ,  telephone,  Marzi,  148 
—  ,  telephone,  rotary  inductor  type, 

192,  193 

— ,  telephone,  Vanni,  149,  151 
Rein,  H.,  51,  52 
Reisz,  E.,  82,  88,  155 
Resistance,  negative,  of  arc,  22-25,  99 

— ,  negative,  of  dynatron,   99 
Rheinsberg,  Germany   (station),  39 
Rieger,  H.,  211 
Ripple,    commutator,    suppression    of, 

89 

Rome,  Italy   (station),  35 
Rotor,  of  Alexanderson  r.f.  alternator, 

117-120,  122-124 

— ,  of  Arco  r.f.  alternator,  115,  116 
— ,  of  Goldschmidt  r.f.   alternator, 

106,  108,  109 

— ,  of  National  Electric  Signaling 
Company  r.f.  alternator,  119 
120 

Round,  H.  J.,  155,  158,  221 
Ruhmer,  E.,  47,  48,  134 

SACRAMENTO,  CALIFORNIA  (STA- 
TION), 34 

San  Francisco,  California  (station),  34, 
66 


Index 


247 


Sayville,  New  York   (station),  168 
Scheller,  52 

Scheldt-Boon  Company,  Brussels,  147 
Schenectady,  New  York  (station),  124, 

126,  180 

Seattle,  Washington  (station),  66 
Secrecy,  in  r.t.,  17,  18 

,  in  w.t,  18 

Seibt,  G.,  51,  134 

Ship-to-shore,  traffic,  3,  52,  90,  188-192, 

235-237 

Spark,  timed,  of  Marconi,  73-75 
Sparks,  r.f.,  44-75 
Speech,  nature  of,  7,  8 
Speed,   control   of   in   r.f.    alternators, 

107,  121,  122,  208 

Stator,  of  Alexanderson    r.f.    alterna- 
tor, 117-120 

— -,  of  Arco  r.f.  alternator,  114-116 
— ,  of  Goldschmidt     r.f.     alterna- 
tor, 106-108 

Stockton,  California  (station),  34 
Strays,  11,  220-227 

— ,  classification   of  by  intensity, 

223,  224 
— ,  classification    of    electrically, 

224-227 

— ,  interference  with  r.t.,  18-20 
— ,  reduction    by    beat   reception, 

207 
— ,  reduction  by  Dieckmann  cage, 

222,  223 

— ,    seasonal  variation  of,  19,  227 
Stray-to-signal,  ratio,  222 
Ctroboscope,  190,  191 

TAYLOR,  J.  B.,  8 
Telefunken  Company,  Berlin,  37- 
39,  88,  104,   111,  134,   154,  183, 
196,   215,   223. 
Telephone  Manufacturing  Corporation, 

Vienna,  27,  143,  144 
"Tickler,"  coil,  92,  214 
Tolls,  for  r.t.  service,  237,  238,  241 
Torikata,  W.,  62-65 
Traffic,    r.t,    see    also    "Ship-to-shore, 
Train,  Aeroplanes,  Mines"  3,  6,  230- 
241. 

Train,  r.t,  3,  4,  69 
Transcontinental,  r.t.,  3,  238-241 
Transfer,    wire-to-radio,    48,    139,    140, 

142,  204,  235,  238 

Transformer,     r.f.,       for       absorption 
modulation,  179,  180 

,     output,      Alexanderson 

alternator,  125,  206 
Transmitter,  condenser,  141 
Transmitters,  portable,  for  r.t,  241 
Trans-oceanic,  r.t.,  3,  34,  238 
Trapani,  Sicily  (station),  36 
Tripler,    frequency,   Telefunken   Com- 
pany, 114 

Tripoli,  (station),  72 
Tubes,  gas-containing,  82,  88,  155,  156 


u 


Tubes,  vacuum,  see  "Audion,  Dyna- 
tron,  Pliodynatron,  Pliotron,  Relay 
(electron),  Vacuum,  tubes" 

Tuckerton,  New  Jersey  (station),  34, 
107 

Tuning,  to  wave  form,  57,  58,  71 

Turbine,  drive  for  t.f.  alternator,  120- 
122 

"T.  Y.  K.,"  system  of  r.t,  62-65 


LTRAUDION,  SEE  "OSCILLA- 
TOR, VACUUM  TUBE,  DE 
FOREST  CIRCUIT" 


VACUUM  TUBES,  76-102.  See  also 
"Audion,  Dynatron,  Pliodyna- 
tron, Pliotron,  Relay  (elec- 
tron)" 

Vacuum,  thermionic,  81,  82,  220 
Vacuum  tubes,  amplifiers,   see  "Ampli- 
fier, vacuum  tube" 
— ,  exhaustion  of,  81,  82 
— ,  oscillators,    see    "Oscil- 
lator, vacuum  tube" 
— ,  Oxid-coated  filament,  96, 

97,  217-219 
— ,  transmitting,    for    high 

power,  82 

— ,  transmitting,  for  high 
power,  de-  Forest,  92, 
161,  162 

— ,  transmitting,    for    high 
power,  General  Elec- 
tric Company,  93 
transmitting,   for    high 
power,     Lieben-Reisz, 
82,  88,  89,   154,   155 
-,  transmitting,    for    high 
power,  Western  Elec- 
tric  Company,   96,   97 
Vallauri,  G.,  Ill 
Valve,    Fleming,    72,    76-82,    221.      See 

also   "Kenotron" 
Vanni,  G.,  70-72,  149-151 
van  der  Bijl,  H.  J.,  217 
Vibration,  mechanical,  in  r.f.  alterna- 
tors, 118,  124 

Vienna,  Austria  (station),  192 
Vittoria,  Italy   (station),  72 
Voice,  energy  of,  127 

WASHINGTON,  BOWDEN,  46,  56, 
58,  60 

Washington,  D.  C.  (station),  34 
Wave   length,   optimum  for   transmis- 
sion, 205,  206 
Western  Electric  Company,  93,  94,  96, 

161,  166-170,  217-219 
White,  W.  C.,  81,  170-175 
Windage,  in  r.f.  alternators,  120 
Wire  vs.  r.t.,  land  telephony,  5,  6 
—  oversea  telephony,  6 


Y 


OKOYAMA,  E.,   G2-65 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN     INITIAL    FINE     OF     25     CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  Sl.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


REC'D  LD 

DEC  4    1956 


LD  21-50TO-8,'32 


YU     I7O7O 


3762,0  / 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


